OSTEOLOGY AND RELATIONSHIPS OF THE LANTERNFISHES (FAMILY MYCTOPHIDAE) X I 03 ON ICHT NY IN I NOTOLYCHN I NI GYM NOSC OMANI

1 ./' WIC TOPHIN I DIAPHINI

MYCTOPHINAE LAMPANYCTINAE

Tribal relationships within the family Myctophidae, illustrating photophore patterns of repre- sentative species. OSTEOLOGY AND RELATIONSHIPS OF THE LANTERNFISHES (FAMILY MYCTOPHIDAE)

By JOHN R. PAXTON

BULLETIN OF THE NATURAL HISTORY MUSEUM

OF LOS ANGELES COUNTY

SCIENCE: NUMBER 13

JUNE 28, 1972 PROFESSIONAL PUBLICATIONS OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY

The professional publications of the Natural History Museum of Los Angeles County include two series, Contributions and Bulletins. In the past, articles, monographs and cata- logs in the fields of history and science have appeared under various headings—Contribu- tions, Science Series, History Leaflet Series and unnumbered catalogs of exhibitions and collections. To simplify and to standardize matters, all professional publications of the History and Science Division of the Museum will now be issued at irregular intervals either as Contributions, or as Bulletins. The former will contain short, technical papers which may be occasionally gathered in volumes, octavo in size. The latter will contain longer, separate monographs and catalogs, usually quarto in size, although this will depend on the needs of the presentation. Papers in each series are to be numbered consecutively. These papers are original articles and studies based on the collections and work of the Museum, presenting newly acquired information and understanding in the fields of Anthro- pology, Botany, Geology, History, Mineralogy, Paleontology, Technology and Zoology.

GILES W. MEAD, Director Natural History Museum of Los Angeles County

VIRGINIA D. MILLER Editor

All communications concerning science manuscripts, exchange of science publications, and the purchase of science publications should be sent to the Editor, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007. TABLE OF CONTENTS

INTRODUCTION 1 Historical Review 3 Acknowledgments 4

MATERIALS AND METHODS 5

OSTEOLOGY 9 Superficial Dermal Bones 9 Mandibular Arch ...... 12 Palatine Arch ...... 17 Hyoid Arch ...... 19 Opercular Apparatus 23 Branchi al Arches ...... 24 Pectoral Girdle 28 Pelvic Girdle 31 Axial Skeleton ...... 32 Caudal Skeleton 32

LUMINESCENT ORGANS ...... 37

Luminous Tissue ...... 37 Photophores ...... 38

THE EVOLUTIONARY LINEAGES ...... 40 Key to the Supraspecific Taxa ...... 51

EVOLUTIONARY RELATIONSHIPS ...... 54 Familial Affinities ...... 54 Subfamilial Relationships ...... 56 Tribal Relationships 58 Generic Relationships ...... 63

EVOLUTIONARY SIGNIFICANCE OF PHOTOPHORE PATTERNS ...... 73

LITERATURE CITED ...... 78 ••■ OSTEOLOGY AND RELATIONSHIPS OF THE 1 LANTERNFISHES (FAMILY MYCTOPHIDAE)

By JOHN R. PAXTON2

ABSTRACT: Analyses of the osteological features, except the neurocra- nium and axial skeleton, and the luminescent organs of representatives of all currently recognized genera in the family Myctophidae revealed a number of evolutionary trends and groups within the family. The subfamilies Mycto- phinae and Lampanyctinae differ in the number of extrascapular elements, the presence or absence of a shelf on the cleithrum, the number and position of the Pic photophores, and the shape of the larval eyes. Two tribes, the Myc- tophini and the Gonichthyini, within the Myctophinae differ in the shape of the antorbital bone, the length of the jaw, the fusion of the procurrent caudal rays, and the position of the mouth and PLO photophore. The Myctophini includes the genera Protomyctophum, Electrona, Diogenichthys, Benthosema, Hygophum, Myctophum, and Symbolophorus; the Gonichthyini includes Loweina, Tarletonbeania, Gonichthys, and Centrobranchus. Four tribes, the Notolychnini, Lampanyctini, Diaphini, and Gymnoscopelini, comprise the subfamily Lampanyctinae. The monotypic Notolychnini displays some char- acters of each subfamily. The remaining three tribes differ in the number, shape, or position of the procurrent caudal rays, distal pectoral radials, supra- maxillary, dentary teeth, and Dn, PO, and PVO photophores. The Lam- panyctini includes the genera Lam padena, Taaningichthys, Bolinichthys, Lepidophanes, Ceratoscopelus, Stenobrachius, Lampanyctus, and Triphoturus. Diaphus and Lobianchia comprise the Diaphini and Lampanyctodes, Gymno- scopelus, Notoscopelus, Scopelopsis, Lampichthys, and Hintonia the Gymnoscopelini. Osteological evidence indicates that myctophids are most closely related to and probably derived from the family Neoscopelidae. A supramaxillary is present in some species, as is a foramen in the ceratohyal, features not pre- viously reported for the family. Osteological trends within the family include streamlining of the body in the Gonichthyini, lengthening of the jaws, sculp- turing of the circumorbitals, and fusion of the extrascapulars in the Lam- panyctinae, increase in the number of procurrent caudal rays and develop- ment of a supramaxillary in the Gymnoscopelini, and a fusion of these rays in a number of lines. Changes in photophore pattern and development of secondary luminous structures closely parallel the osteological trends apparent in the various lineages and the phylogeny presented is basically similar to those previously proposed on the basis of photophore patterns alone.

INTRODUCTION Myctophids undertake extensive vertical migra- tions; in one study they were found to range diur- Lantemfishes of the family Myctophidae are nally from 400 to 750 meters and nocturnally to world-wide in distribution and are found in the the upper 100 meters (Paxton, 1967a). Many midwater regions of all major oceans. Myctophids species are taken at the surface under a night-light, are the most speciose of midwater fish families with more than 300 nominal species and probably about 200 valid species. In a long-term trawling 'EDITORIAL COMMITTEE FOR THIS BULLETIN Robert J. Lavenberg project off Bermuda, these representatives of the H. Goeffrey Moser order Myctophiformes (Iniomi, Scopeliformes) Basil G. Nafpaktitis were second only to the bristlemouth Cyclot hone of Camm C. Swift the family Gonostomatidae in the number of speci- 'The Australian Museum, Sydney, New South Wales, mens captured (Beebe, 1937) ; in many areas, Australia; and Research Associate in Ichthyology, lantemfishes make up the largest fish biomass of a Natural History Museum of Los Angeles County, Los midwater trawl catch. Angeles, Calif. 90007.

1 2 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 while a very few forms apparently undergo no phology and position of body photophores do not vertical migration. Studies on the migration pat- suggest their adaptive significance, and several terns and swimbladder structure have indicated that hypotheses have been advanced to explain the lanternfishes are important contributors to the relatively common occurrence of luminous organs sonic scattering layers; bathyscaphe observations or tissue on the bodies of deep sea fishes. Harvey have confirmed that their migrations correspond (1952) and McAllister (1967) have made the to the scattering layer migrations (Barham, 1966; most extensive, recent reviews on the subject. Backus et al., 1968). Recent captures indicate None of the proposed hypotheses have been some species are associated with the bottom and tested experimentally in midwater fishes, because not restricted to the midwaters. none can presently be maintained alive for any Myctophids are utilized as a food source by length of time. In the shallow water midshipman many larger organisms, including a number of Porichthys, photophore display during courtship commercially important fishes. Lanternfishes them- has been reported (Crane, 1965). Most species of selves consume primarily crustaceans, although the family Myctophidae have a distinctive photo- larger individuals occasionally take small fishes phore pattern; specific identification is often based (Paxton, 1967b). The adult size range for the upon the pattern. In those groups where the pattern family is considerable; some species mature at less of body photophores is little varied, the luminous than 20 mm, while others reach more than 200 mm organs on the head are often unique for each standard length. Little is known about the repro- species. While the original adaptive value resulting ductive biology of lanternfishes. One report of fer- in the formation of photophores may have been tilized eggs within a female (Grey, 1955) has never any of a number of functions, the numerous varia- been confirmed. Although myctophid eggs are tions in photophore placement in myctophids rarely taken in plankton nets, their small size and suggests that in this group photophores function fragile nature may preclude net capture of identi- primarily to maintain the reproductive isolation of fiable specimens (Moser and Ahlstrom, 1970) ; each species. internal fertilization is not indicated by adult mor- Previous taxonomic studies on the family Mycto- phology. Some species apparently are reproduc- phidae primarily have utilized the variations in tively active for as long as six to nine months in a photophore patterns to distinguish evolutionary year (Paxton, 1967b). groupings. Currently 30 genera are recognized The most characteristic feature of lanternfishes within the family. The most recent generic defini- is the presence of light organs or photophores, that tions and relationships proposed by Fraser-Brunner are usually restricted to the ventral half of the body. (1949), as in other works on lanternfishes, are The patterns of photophores on the body are based almost entirely on photophore patterns. If usually specifically distinct. The individual photo- the species-recognition hypothesis for photophore phores are complex structures, complete with light function in myctophids is valid, photophores should gland, reflecting layer, and lens (Marshall, 1965). be excellent taxonomic characters at the specific No luminescent bacteria have ever been cultured level, and as such they have been utilized exten- from myctophid photophores; self-produced light sively. However, an interpretation of the evolution- is indicated by their morphology. Organs of the ary history of the group above the species level may trunk and tail are innervated by branches of the be open to question when primarily based upon spinal nerves (Ray, 1950). In addition to photo- such a plastic set of characters. Internal anatomy, phores, various lanternfishes have luminous tissue, particularly nerves and bones, is known to be rela- which may include well-developed orbital organs tively conservative evolutionarily. Yet all of the anterior and ventral to the eye, discrete luminous previous studies on internal anatomy have either glands, particularly on the caudal peduncle, lumi- been restricted to one or a few species, or the find- nous patches on various parts of the body, and ings have not been used to determine evolutionary minute secondary photophores associated with each relationships, or the characters discovered have scale. been used at the familial level or higher. The functions of luminous organs in fishes have The present study proposes to describe and long been a matter of conjecture. The functional analyze the osteology of all of the currently recog- significance of certain light organs can be inferred nized genera within the family Myctophidae and to from their morphology and position on the body. elucidate the evolutionary history of this group of The luminous escas of anglerfishes and chin barbels fishes. The study has five primary objectives: 1) to of dragonfishes are probably utilized to lure food describe the osteological variation within the fam- organisms near the mouth. However, the mor- ily; 2) to broaden the definitions of the evolu- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 3 tionary lineages to include characters of osteology; apparently the first to raise the neoscopelids to 3) to determine the major evolutionary trends familial rank; most recent systematic works concur within the family; 4) to assess the relationships of (Marshall, 1955; Bolin, 1966; Gosline et al., 1966; the various evolutionary lineages; and 5) to exam- Greenwood et al., 1966; Rosen and Patterson, ine the significance of photophores in the evolu- 1969). Wisner (1963b) erected the tribe Elec- tionary history of the family. tronini for four genera within the family. No other The relationships of the family Myctophidae to tribal or subfamilial categories have been proposed. other lower teleost families are still open to ques- The latest familial revision is that of Fraser- tion (Gosline et al., 1966; Greenwood et al., 1966; Brunner (1949); 24 genera and 11 subgenera were Rosen and Patterson, 1969). As Jollie (1954) recognized and the species were treated on a world- stated "An account of the anatomy of one species wide basis. Recent contributions (Bolin, 1959; will open the way for an anatomical survey of the Andriashev, 1962; Wisner, 1963b; Hubbs and Family Myctophidae and ultimately the Order Wisner, 1964; Nafpaktitis, 1966; and Nafpaktitis Iniomi. It is by this method of advancing from a and Paxton, 1968) have increased the number of known center that an investigation of the group can genera to 30, with two additional subgenera. Most logically be carried out." The present study is the of the newly recognized genera were considered next step. subgenera by Fraser-Brunner (1949). HISTORICAL REVIEW Previous anatomical studies on lanternfishes, with an emphasis on osteology, are summarized Rafinesque described the first lanternfish, Mycto- below. Supino (1901) described the cranial oste- phum punctatum, from the Mediterranean Sea in ology of Scopelus benoiti (=-Hygophum benoiti). 1810. Since the time of Regan (1911), the family Since his staining techniques were unsatisfactory, Myctophidae has been included in the order Myc- his descriptions were based primarily on sections tophiformes (Iniomi, Scopeliformes). Regan gave of unstained material. The stated purpose of the the following osteological definition of the order: study was to assess a possible correlation between pelvic bones free from cleithra; premaxillaries the large amount of cartilage reported in the skull exclude maxillaries from gape; pectoral girdle and the effect of the "great depths" at which the attached to skull by forked posttemporal; no meso- species was thought to live. The myctophid skull coracoid; vertebral centra co-ossified with arches. was compared with those of Chauliodus sloanei Regan separated the order into two suborders, and Argyropelecus hemigymnus. An osteological the Alepisauroidea and Myctophoidea; other definition of the family was presented by Regan families in the Myctophoidea include Aulopidae, (1911). He based his characters primarily on Synodontidae, Harpadontidae, Bathysauridae, Neoscopelus, which is now placed in the family Chlorophthalmidae, Bathypteroidae, Ipnopidae, Neoscopelidae, although he examined Lam panyc- Neoscopelidae, and Notosudidae (Gosline et al., tus (a myctophid) and stated the two were very 1966). Recently Greenwood et al. (1966) rele- similar. The osteological definition included parie- gated the entire order to a subordinal level within tals separated by supraoccipital, posterior temporal the order Salmoniformes (Isospondyli), because no fossae not roofed, no orbitosphenoid, slender para- characters will consistently separate all members of sphenoid meeting frontals, lateral ethmoids sepa- the two suborders (Marshall, 1955) . However, rated by parasphenoid and below parasphenoid, other authors (Gosline et al., 1966; Rosen and and mesethmoid with a prominent median ridge. Patterson, 1969) are convinced that the integrity Parr (1929) described the osteology and com- of the group warrants ordinal recognition, and such pared four families of the order Iniomi, but a treatment is followed in this study. specifically excluded consideration of the Mycto- Prior to the work of Goode and Bean (1896) , phidae. Gregory (1933) included only a figure of the family included most forms now placed in the the skull of a postlarval Myctophum humboldti order Myctophiformes (Iniomi). Goode and Bean (=- M. punctatum?) in his treatise on fish skulls. limited the family to those genera placed in the Fraser-Brunner (1949) used the absence of a family by Fraser-Brunner (1949), plus Scopelo- supramaxillary and the placement of the anal fin saurus, which Regan (1911) subsequently removed. under or slightly behind the dorsal fin, rather than Fowler (1925) erected the subfamily Neosco- far behind the dorsal as characters to differentiate pefinae for Neoscopelus. Fraser-Brunner (1949) myctophids from neoscopelids. Harry (1952) dis- considered the Neoscopelinae to include Neoscope- cussed the relationships of iniomous families, but lus, Scopelengys, and the monotypic Solivomer, presented no new morphologic data. Jollie (1954) described by Miller (1947). Smith (1949) was described the general anatomy, including a detailed 4 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No.13 study of the osteology, of the lanternfish Lam- Other anatomical studies include a comprehen- pan yctus leucopsarus ( =Stenobrachius leucopsar- sive account of the microscopic structure of the us). He utilized dissected, cleared and stained, eyes, photophores, and caudal luminous glands of and sectioned material in his impressive work. many species of lanternfishes (Brauer, 1908) ; the Marshall (1955) compared the families of the two peripheral nervous system of Stenobrachius leucop- suborders of myctophiform fishes. Although most sarus (Ray, 1950); general anatomy of the same of his discussion was on the alepisauroid families, species (Jollie, 1954); and the swimbladder struc- he noted that complete squamation and usually ture of 21 species of myctophids in 14 genera high position of the pectoral fins were found in (Marshall, 1960). myctophids, but in few other pelagic representa- tives of the order. Rosen (1964) figured and dis- ACKNOWLEDGMENTS the caudal skeleton of Myctophum affine. cussed I am most grateful to Jay Savage of the Univer- Berry (1964) briefly described the upper jaw devel- sity of Southern California (USC) for his original opment in Lampanyctus. Gosline (1961) and suggestion of the problem, continued advice and al. (1966) discussed the relationships Gosline et encouragement, and critical review of the manu- of a number of lower teleost families, including script. Thanks are due Basil Nafpaktitis (USC) myctophids, in the light of osteological features. for his gift of specimens while still at Harvard Uni- Characters of the skull, pelvic girdle, and caudal versity, numerous thought provoking discussions, skeleton were described. Patterson (1964) briefly and review of the manuscript. Leslie Chambers, discussed the relationships of myctophids and acan- John Garth, and Donn Gorsline (USC) criticized thopterygians, based primarily on fossil forms. an early version of the manuscript. The following Greenwood et al. (1966) discussed the ordinal individuals exchanged or donated specimens for the relationships of teleost fishes; a number of neo- present study: Giles Mead and Myvanwy Dick, scopelid characters were described, but mycto- Museum of Comparative Zoology, Harvard Uni- phid morphology was not specifically discussed. versity; Daniel Cohen and Bruce Collette, Bureau McAllister (1968) described the hyoid arch and of Commercial Fisheries, Washington, D.C.; branchiostegal rays of myctophids, as well as those Ernest Lachner, U.S. National Museum (USNM); of many other teleost groups. Rosen and Patterson C. Richard Robins and Thomas Devany, Univer- (1969) described various osteological features of sity of Miami Marine Laboratory; Frederick Berry the upper jaw, hyoid arch, occipital region of the and William Richards, Bureau of Commercial neurocranium, median fins, and caudal skeleton of Fisheries, Miami; Richard Grinols, University of myctophids in their discussion of familial and ordi- Washington; William Pearcy and Leonard Cole- nal relationships. Thirteen lanternfish species rep- man, Oregon State University; John Fitch, Cali- resenting seven genera were examined in their fornia Fish and Game; Robert Lavenberg, Natural study. Moser and Ahlstrom (1970) have described History Museum of Los Angeles County; Robert larvae of 14 species of lanternfishes from Califor- Wisner and Richard Rosenblatt, Scripps Institu- nia and reviewed previous work on myctophid tion of Oceanography; Elbert Ahlstrom and larvae. Osteological development is described and H. Geoffrey Moser, Bureau of Commercial Fish- larval characters are used in an illuminating dis- eries, La Jolla; Eugene Nakamura, Bureau of Com- cussion of generic relationships. mercial Fisheries, Hawaii; Michael Penrith, South A number of otoliths from Recent species African Museum; and John Moreland, Dominion have been described and figured by Frost (1926), Museum of New Zealand. I extend my thanks to Lavenberg and Fitch (1966), Nafpaktitis and the many scientists from the University of Southern Paxton (1968), and Fitch (1969), among others. California and the Allan Hancock Foundation and Many fossil otoliths have been characterized and the crew members who participated in cruises of 16 fossil genera have been allocated to the family the R/V Velero IV and the USNS Eltanin. Various Myctophidae according to the summary of Romer aspects of the problem were discussed at length (1966: 356) ; however, it is probable that a number with Elbert Ahlstrom, H. Geoffrey Moser, John of forms cannot be referred to the family, as cur- Fitch, Rolf Bolin of Hopkins Marine Station, rently restricted. David (1943) figured species of William Gosline of the University of Hawaii, Recent genera from the Miocene of southern Cali- Stanley Weitzman and W. Ralph Taylor of the fornia, in which distinct photophores are apparent. U.S. National Museum, and fellow graduate stu- The recent study of Goody (1969) on Cretaceous dents Robert Lavenberg and Richard McGinnis. myctophoids does not include any members of the Unpublished manuscripts were kindly made avail- family Myctophidae. able by Moser and Ahlstrom, Gosline, Taylor, and 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 5 by D. E. McAllister of the National Museum of andriashevi 2(44-46); LACM 10918-3; AMS Canada. Weitzman thoughtfully criticized portions 1.16029-001 arcticus 3(19-40); LACM 10009-8; AMS of the manuscript and Collette kindly reviewed the 1.16032-001 entire paper. My wife, Hannelore, translated vari- bolini 4(31-51); LACM 10884-7; AMS ous articles and typed earlier versions of the man- 1.16030-001 uscript. To all I extend my sincere appreciation. crockeri 8(15-43); LACM 9034-28, 9806-20, The study was supported in part by NSF grants 9815-29, AMS 1.16033-001 normani 3(51-55); LACM 10837-3, 10906-4; G-23647 and USARP GA-238, Jay M. Savage, AMS 1.16031-001 principal investigator. parallela 4(28-47); LACM 10399-11, 10836-9; AMS 1.16034-001 MATERIALS AND METHODS subparallela 3(25-46); LACM 11075-5; AMS 1.16035-001 Two relatively recent technical advances have thompsoni 1(50); LACM 32198-1 enhanced the present study. The first is the wide- Electrona 6-7 spread use of the high speed Isaacs-Kidd Midwater rissoi* 2(47-72); LACM 32223-1; AMS Trawl in midwater sampling (Deveraux and Win- 1.16036-001 ahlstromi ? 1(61); LACM 11330-5 sett, 1953) , that has resulted in the accumulation antarctica 5(28-84); LACM 10892-3; AMS of thousands of lanternfish specimens in numerous 1.16037-001 collections. The continuing midwater collections carlsbergi 4(16-68); LACM 10851-1, 10976-14; made by the University of Southern California off AMS 1.16038-001 the coast of southern California and northern paucirastra 3(27-59); LACM 10365-8, 10974-10; AMS 1.16039-001 Mexico aboard the V elero IV and in the southern subasper 2(26-70); LACM 11574-1; AMS oceans aboard the Eltanin have resulted in an ex- 1.16040-001 tensive study collection of midwater fishes. Hygophum 7-8 The species utilized are listed below under the atratum 4(43-61); LACM 8863-7 hanseni 4(34-44); LACM 10613-4; AMS genera recognized in this study. For convenience in 1.16041-001 the osteological analysis, the subgenera Hierops proximum 2(39); LACM 31334-5; AMS and Nasolychnus are treated as genera. Following 1.16042-001 the genera are the approximate number of valid spe- taaningi 2(36-43); LACM 32218-1; AMS cies, both described and undescribed. Following 1.16043-001 Benthosema 5-6 each species name designation is the number of glaciale* 5(41-58); LACM 10009-10, 11546-6; cleared and stained specimens studied, their mini- AMS 1.16044-001 mum and maximum standard lengths in millimeters panamense 2(26-34); LACM 8828-3 and the museum registration numbers. Type-species suborbitale 2(23-26); LACM 32222-1; AMS 1.16045-001 of the genera are marked by an asterisk. Compara- Diogenichthys 3 tive material in families other than Myctophidae laternatus* 3(24-26); LACM 8807-10 were examined in much less detail. All species were atlanticus 4(17-23); LACM 9034-27, 10023-2, identified from the literature, with the aid of an 32197-1; AMS 1.16046-001 panurgus 2(16-22); LACM 31334-4; AMS unpublished key to the genus Lampanyctus pre- 1.16047-001 pared by Rolf Bolin, and through the use of Myctophum 14? comparative material. Basil Nafpaktitis kindly affine 2(39-42); LACM 32213-2; AMS identified north Atlantic species of the genera 1.16048-001 Lobianchia and Diaphus. Most of the collection, asperum 2(63-71); LACM 32213-1; AMS 1.16049-001 including all dissected myctophids, is on deposit aurolaternatum 2(35-39); LACM 32203-1 in the Natural History Museum of Los Angeles brachygnathum 1(79); LACM 32187-1 County (LACM). Representatives of some species lychnobium 3(70-84); LACM 32228-1; AMS are deposited in the Australian Museum, Sydney 1.16051-001 nitidulum 3(39-68); LACM 9904-3; AMS (AMS), as well as the National Museum of Natu- 1.16052-001 ral History (USNM). phengodes 1(57); LACM 32232-1 Symbolophorus 10? Myctophidae californiensis* 5(41-74); LACM 6764-21, Protomyctophum 12 6766-27, 9904-4, 31666-5; AMS 1.16053-001 tenisoni* 5(41-74); LACM 10555-3, 10892-2, boops 5(25-111); LACM 10365-7, 11575-1, 10931-4; AMS 1.16027-001 11576-1; AMS 1.16054-001 anderssoni 33(14-70); LACM 10028-8, 10388-6, evermanni 3(63-73); LACM 32227-1; AMS 10551-3, 10580-4, 10672-7, 10675-5, 10842-4, 1.16055-001 10861-6, 10924-5, 10961-6, 11561-6; AMS species a 3(65-73); LACM 32196-1; AMS 1.16028-001 1.16056-001 6 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No.13

Loweina 4? idostigma 5(32-81); LACM 8863-6; AMS rara* 3(30-35); LACM 32183-1, 32226-1; 1.16083-001 AMS 1.16057-001 ingens 4(67-135); LACM 9300-46, 9927-20; Tarletonbeania 1-2 AMS 1.16079-001 crenularis* 5(28-55); LACM 9030-16, 9639-19; intricarius 2(81-111); LACM 10613-3; AMS AMS 1.16058-001 1.16084-001 Gonichthys 4 iselinoides 4(30-79); LACM 10365-6; AMS tenuiculus 4(20-40); LACM 32215-1, 32229-1 1.16085-001 Centrobranchus 4 jordani 2(58-104); LACM 32200-1; AMS choerocephalus* 2(32-37); LACM 32190-1, 1.16086-001 AMS 1.16059-001 macdonaldi 2(75-98); LACM 10009-9; andrae 1(51); LACM 32216-1 AMS 1.16087-001 Lobianchia 3? omostigma 2(49-50); LACM 32225-1; AMS gemellari* 2(55-57); LACM 32186-1; 1.16088-001 AMS 1.16060-0017 parvicauda 2(66-89); LACM 8807-9 dofieini 2(26-34); LACM 32191-1; regalis 5(50-150); LACM 8989-32,9003-37, AMS 1.16061-001 9762-32; AMS 1.16089-001 Diaphus 50? ritteri 5(43-83); LACM 6766-26, 30459-18; theta* 5(25-56); LACM 6764-20, 9499-20, AMS 1.16090-001 9639-20, 31666-4; AMS 1.16062-001 Lepidophanes 2 dumerili 2(47-48); LACM 32214-1; AMS guentheri* 1(57); LACM 32194-1 1.16063-001 Bolinichthys 5? elucens 1(38); LACM 32219-1 longipes* 6(33-45); LACM 9939-12, 32201-1; fragilis 2(40-49); LACM 32219-2; AMS AMS 1.16091-001 1.16064-001 Ceratoscopelus 3 garmani 3(30-50); LACM 32188-1; AMS maderensis* 2(62-64); LACM 32202-1; AMS 1.16065-001 1.16092-001 luetkeni 2(43-47); LACM 32184-1; AMS townsendi 4(42-65); LACM 8988-36, 9367-30; 1.16066-001 AMS 1.16093-001 metopoclampus 1(44); LACM 32185-1 Gym noscopelus 9 ,no//is 2(28-37); LACM 32211-1; AMS aphya* 5(28-124); LACM 10369-4, 10904-1; 1.16067-001 AMS 1.16094-001 ostenfeldi 2(75-85); LACM 10833-2; AMS bolini 2(73-203); LACM 10618-5; AMS 1.16068-001 1.16095-001 pacificus 3(20-30); LACM 32189-1; AMS braueri 3(56-110); LACM 10555-4; AMS 1.16069-001 1.16096-001 splendidus 2(47-60); LACM 32195-1; AMS f raseri 3(49-80); LACM 10416-7; AMS 1.16070-001 1.16098-001 Notolychnus 1 opisthopterus 3(35-96); LACM 10028-7, 10355-6; valdiviae* 4(21-24); LACM 8992-34, 32193-1 AMS 1.16097-001 Taaningichthys 3 piabilis 3(60-111); LACM 10362-13, 10666-5; bathyphilus* 2(64-65); LACM 9578-24; AMS AMS 1.16099-001 1.16072-001 species a 3(57-61); LACM 10833-1; AMS minimus 2(55-58); LACM 32221-1; AMS 1.16100-001 1.16073-001 species b 3(51-56); LACM 10362-12; AMS Lampadena 10 1.16101-001 urophaos 3(63-91); LACM 6523-16, 9878-5; species c 1(107); LACM 10864-4 AMS 1.16074-001 Lampichthys 1 Lampanyctodes 1 procerus* 2(66-73); LACM 11076-17; AMS hectoris* 6(32-58); LACM 10969-4; AMS 1.16102-001 1.16075-001 Notoscopelus 6 Stenobrachius 2 resplendens* 2(65-73); LACM 9350-25; AMS leucopsarus* 6(31-76); LACM 9639-18, 9938-29; 1.16103-001 AMS 1.16076-001 caudispinosus 1(74); LACM 32217-1 nannochir 3(89-107); LACM 32198-2; AMS Hintonia 1 1.16077-001 candens* 3(51-56); LACM 10362-14, 10363-10; Triphoturus 3-4 AMS 1.16104-001 mexicanus 12(26-66); LACM 6503-11, 8988-37, Scopelopsis 1 9639-21, 9858-15; AMS 1.16078-001 multipunctatus* 2(47-50); LACM 32220-1; nigrescens 1(37); LACM 32192-1 AMS 1.16105-001 Lampanyctus 40? Neoscopelidae crocodilus* 1(160); LACM 32230-1 Neoscopelus macrolepidotus 2(65-90); LACM achirus 5(77-134); LACM 10836-8, 10873-6; 32231-1; AMS 1.16106-001 AMS 1.16080-001 Scopelengys tristis 2(122-125); LACM 9497-20; australis 5(30-97); LACM 10363-9; AMS AMS 1.16107-001 1.16081-001 Solivomer arenidens 1(98); USNM 135419, paratype hubbsi 2(59-65); LACM 32224-1; AMS Chlorophthalmidae 1.16082-001 Chlorophthalmus agassizi 1(112); AMS 1.16108-001 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 7

Parasudis truculentus 1(160); AMS 1.16109-001 original description. Through the kindness of Synodontidae Dr. L. Sorbini of Naples I have recently received a Synodus poeyi 2(62-83); LACM 6295 xerox of Costa's article and figures. The specimen Notosudidae Scopelosaurus cf. harryi 1(67); LACM 9640-26 described is definitely not a member of the family Bathypteroidae Myctophidae, but appears to be a clupeoid fish, Bathypterois bigelowi 1(109); AMS 1.16110-001 possibly an engraulid. The following characters Scopelarchidae mitigate against placement of the genus in the Myc- Scopelarchoides nicholsi 1(102); LACM 8274 Paralepididae tophidae intermaxillaries weak, completely lacking Lestidium ringens 1(114); LACM 9002-5 teeth; maxillaries with small teeth; scales with dis- Cetomimidae tinct wavy lines; silver lateral stripe; and the pres- Gyrinomimus grahami 1(141); LACM 10407-3 ence of scales but no mention of photophores. The Rondeletiidae following combination of characters, seven ventral Rondeletia loricata 1(94); LACM 9254-33 rays, indistinct lateral line, and slightly subterminal Recently Coleman and Nafpaktitis (1972) have mouth are found only in myctophid fishes of the described a new genus of myctophid, Dorsadena, tribe Gonichthyini; however no species of this tribe based upon one new species from the eastern north has the jaws extending more than an eye diameter Pacific. The lack of available specimens precludes behind the orbit as shown in the figure of Cyrto- an osteological examination at the present time. rhynchus. Most of the above characters fit clupeoid Dorsadena is considered to be a close relative of fishes (Costa describes the structure of the scales as Lam padena and will be discussed in the section on analogous to those of Clupeidei, order Cichloidei); relationships. the long jaws and slightly overhanging snout Certain genera not recognized here or in the strongly imp:icate an engraulid fish. However one synonymies in a later chapter were listed by Jordan character, the description of an adipose fin, is never (1923) and Golvan (1965) as Recent genera of found in any clupeoid and may have been the cause the family Myctophidae. These include Macro- of the erroneous placement of the genus in the stoma Risso 1826, Phanerobranchus Cocco 1846, Myctophidae. A translation of Costa's description Cyrtorhynchus Costa 1855, Protoblepharon Steche of this feature reads "A small distance behind it 1909, and Mystibranchus Whitley 1939. Cypho- [the dorsal fin] is found a rudimentary adipose fin, scopelus Fowler 1925 will be discussed in a later consisting of folded skin, which is concealed in a chapter. Bolin (1939:128) has shown that Macro- furrow corresponding to its length and depth." His stoma Risso 1826 is not a myctophid, but may be a figure shows a very small projection, longer than clupeid. The original description of Phanero- high and three and one-half times closer to the dor- branchus has not been available to me. To my sal base than the caudal base. In light of all the knowledge, the name has not been used for myc- other characters mentioned above, this feature is tophids since the period of its original designation probably the result of an injury, perhaps during and placement within the family cannot be con- capture, and does not represent a true adipose fin. firmed or denied. If, by study of the type speci- Its position, so close to the dorsal base over the men, the name is found to be a senior synonym of middle of the anal fin, is unlike that of any myc- some currently recognized generic name, an appli- tophiform fish. Another apparent error in the text cation for a nomen oblitum ruling would be appro- is the description of the anal fin as "composed of priate. Phanerobranchus Cocco 1846 is preoccu- eight simple rays and a very small spiny one an- pied (Phanerobranchus Leuckart 1821, Urodela); terior." This low number not only excludes all Whitley (1939) proposed Mystibranchus to replace known myctophids, but also all clupeoids. How- the preoccupied name, but gave no hint as to the ever, the figure shows a long-based anal fin with affinities of the genus under question. about 23 rays depicted. In summary Cyrtorhynchus In 1855 Costa described a new genus and species leopoldi is not a member of the Myctophidae, but of fish, Cyrtorhynchus leopoldi, from the Gulf of is probably an engraulid fish. Protoblepharon Naples. Costa did not place the new genus in a Steche 1909 is apparently a lapsus calami by Jordan family, but gave a three page description, plus fig- (1923). Steche (1909) wrote on the light organs ures of the lateral view of the whole specimen, dor- of Photoblepharon Weber 1902, an anomalopid sal view of the head and branchial basket, and lateral views of three scales. Both Jordan (1923) fish. Nowhere in the article was the generic name and Golvan (1965) in their respective surveys of spelled Protoblepharon, and myctophids were men- fish genera, as well as Norman (1966), have placed tioned only briefly as comparative material. The Cyrtorhynchus in the family Myctophidae. I have name is an invalid subsequent spelling (Anon., found no other references to this genus since the 1961: Art. 33) and has no nomenclatural status. 8 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

The second advance that materially contributed Harrington, 1955; Gosline, 1960, 1961; Weitzman, to this study was the development of a clearing 1962, 1967a). The terminology used by Supino technique utilizing the enzyme trypsin (Taylor, (1901) is somewhat different than that used here; 1967). Skin, muscle, and connective tissue must the differences are primarily historical and will not become transparent to enable study of the stained be discussed. bones and the usual clearing method utilized a solu- Each bone and most of the variation for the tion of KOH (Hollister, 1934 ) . This method individual elements found within the family are proved unsatisfactory for lanternfishes; specimens described. To reduce the necessity of long lists of either did not clear completely or became disarticu- genera within the text, tables have been prepared lated in the process. that indicate the variation in a series of bones for Specimens were identified, measured, eviscer- each of the genera. All genera recognized prior to ated, scaled, and tagged prior to clearing. The the commencement of this study are listed and the method of Taylor (1967) was utilized with the subgenera Hierops and Nasolychnus are considered following modifications: just before staining, all genera. Hierops includes the species arcticus, crock- specimens were carried in steps through absolute en, parallela, sub parallela and thornpsoni, while ethanol to dissolve undigested fat, and a 70 per cent Nasolychnus includes the species fraseri?, piabilis, isopropanol-base alizarin stain solution with a few a, b and c. In many cases, the choice of a category drops of 3 per cent KOH was used for staining is arbitrary; many variations are part of a trend and (a 3 per cent KOH stain solution resulted in dis- the dividing lines between slightly, moderately, and articulated specimens). Individual specimens were well developed or small, medium, and large, for stored in 100 per cent glycerine. instance, are difficult to discern. Where possible an Dr. Stanley Weitzman kindly demonstrated a osteological landmark (e.g., the extension anterior dissection technique which proved most satisfac- or posterior to a particular element) is used to tory. With micro-dissection tools, the pectoral girdle reduce subjectivity. The presence or absence of a is cut free in one piece from the left side; the given bone or even a portion of a bone is all too symphysis of both jaws is severed, as is the left infrequent. interhyal; the left upper and lower jaws, nasal, The limitations of the study influence the results antorbital, circumorbitals, palate, and suspensorium obtained and must be pointed out. The first, as are removed as a unit; the hypobranchial skeleton mentioned above, is the subjectivity inherent in is removed entire, as is the pelvic girdle. The dis- assigning categories. An obvious solution to the section results in a five piece skeleton and bone problem is to utilize characters about which there relationships can be conveniently studied. One spec- is no question, such as the presence or absence imen of each of the 98 lanternfish species and 12 of an element. Such a treatment would drastically non-myctophid species were thus dissected and, reduce the number of characters under analysis with one additional specimen of five myctophid and materially lessen the value of the study. species, formed the core of the study collection. Another problem is the recognition of correlated The remainder of the 341 cleared and stained characters. For instance, many cranial elements specimens were examined for variation in less apparently change shape as the length of the jaws detail. behind the orbit changes. If these correlated char- The specimens were examined under a stereo- acters are considered singly and given equal impor- scopic dissecting microscope at 10 to 90 power. tance, undue weight is effectively given to a single, The drawings were made with the aid of a micro- though complex, evolutionary change. projector and a camera lucida. Usually two figures The range in size of adult specimens in the fam- of each bone or series of bones are presented to ily is reflected in the osteological characteristics of demonstrate the variation described and reduce the the species. While most species mature between 40 amount of detailed description necessary. and 80 mm, some species of the genera Diogenich- Most of the bone nomenclature used in this study thys, Diaphus, and Notolychnus mature at and follows Jollie (1954). The accurate osteological apparently grow no larger than 25 mm. Some spe- descriptions in his study were a great aid in the cies of Diaphus, Lam padena, Lampanyctus, and present work. In other cases, the derivation of the Gymnoscopelus reach a size considerably larger name used is discussed. When the homology of a than 100 mm; a 203 mm specimen of Gymno- given element is currently in question, for instance, scopelus was the largest cleared and stained. Juve- the posterior elements of the lower jaw, the vomer, nile characteristics may be retained in the small and the frontals and parietals, the usage in recent species. While a wide range of sizes was not exam- ichthyological works is generally accepted (see ined for most species, juvenile and adult examples

1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 9 of a few species were studied in the hope of gaining some insight into the problem. Much the same type of difficulty is encountered between species with different amounts of ossification. In any study of this kind, time and practicality dictate what is to be included and what excluded from consideration. In the present analysis, two functional units of the lanternfish skeleton, the cranium proper and the axial skeleton, except the 1 mm caudal skeleton, are excluded from consideration. Since the present study is primarily concerned with FIGURE 1. Lateral view of left nasal and antorbital relationships at the generic level and above, diag- bones. A. Scopelopsis multipunctatus, 50 mm. B. Cen- noses and descriptions of individual species are not trobranchus choerocephalus, 37 mm. AD—antorbital; attempted. Critical species will be discussed in the NA—nasal. section on evolutionary relationships. Scale char- acteristics, larval features, fossil forms, and biogeo- tral region of the trough; a very slight ridge is also graphic imp'ications, while pertinent, are consid- present in Tarletonbeania. In both genera the ered beyond the scope of the study. trough is considerably narrowed, particularly at the dorsal margin of the bone. In Gonichthys and OSTEOLOGY especially in Centrobranchus, the nasal is strongly Superficial Dermal Bones convex and projects over the maxillary (Fig. 1B); it is the modified nasal which forms the projecting Nasal and Antorbital snout in these forms. In both genera, the outer, Historically, numerous names have been applied anterior wall of the trough is reduced to a small to the bones associated with the nasal organ. The anterodorsal ridge on the edge of the nasal and the anteriormost element has been called the nasal by inner, posterior wall has become greatly expanded most recent authors (Jollie, 1954; Harrington, posterolaterally. 1955; Weitzman, 1962). However, the homologies The antorbital is a small, dermal bone which lies of the posterior element are still uncertain. This between the nasal organ and the lateral ethmoid bone is called the antorbital, following Gosline (Fig. 1). Its ventral portion lies medial to the (1961), Weitzman (1962), and Nybelin (1967), posteroventral region of the nasal and anterodorsal rather than adnasal (Jollie, 1954 and others). to the first circumorbital. The antorbital is held in The nasal, a thin dermal bone, is the most ante- place by connective tissue, which joins the bone to rior of the superficial skull bones. The nasal is the first circumorbital, nasal, and lateral ethmoid. usually shaped like a shallow, open trough (Fig. In Loweina, Tarletonbeania, Gonichthys, and Cen- 1A), and extends from the first circumorbital ante- trobranchus the antorbital is reduced to a small, riorly to the dorsal process of the premaxillary and thin lamina of bone. It is often weakly ossified in dorsally to the anterior margin of the frontal. other forms. The two nostrils open in the space Although the nasal appears to be a continuation between the nasal and antorbital; the posterior nos- of the circumorbital series, the suborbital sensory tril is crescent-shaped and the antorbital forms its canal does not extend forward onto the nasal; the posterior border. Although the orbital luminous supraorbital canal extends onto the snout (Jollie, organs of Diaphus are often extensive, they appar- 1954:26). The posteroventral margin of the nasal ently do not affect the shape of the antorbital or is strongly joined to the anterior margin of the nasal bones. first circumorbital, while the dorsal portion is The antorbital was not reported by Supino bound to the frontal by connective tissue. The inner (1901) in Hygophum benoiti, but is present in all margin of the nasal surrounds the anterior portion myctophids, including the species of Hygophum, of the nasal organ. The outer margin overlies the examined by me. anterior maxillary and premaxillary ventrally and anteriorly, while dorsally the outer margin of the Circumorbitals nasal meets its fellow from the other side in the The circumorbitals (CO) are a series of six midline to form a slight nasal ridge, which com- bones that lie ventral and posterior to the orbit, pletely covers the small ethmoid ridge; the nasal and contribute substantially to the support of the ridge ends at the anterior margin of the frontal. eyeball. Posteriorly, scales usually cover the space The nasal is often weakly ossified. between the last four circumorbitals and the pre- In Loweina, a small ridge projects from the ven- opercle. The shapes of the bones are extremely 10 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

FIGURE 2. Left circumorbital bones of a short-jawed species, Myctophum lychnobium, 84 mm. A. Lateral FIGURE 3. Left circumorbital bones of a long-jawed view. B. Anterodorsal view, modified perspective (bones were moved during drawing), of lateral and species, Gymnoscopelus bolini, 203 mm. A. Lateral Anterodorsal view, modified perspective subocular shelves. view. B. (bones were moved during drawing), of lateral and subocular shelves. variable (Figs. 2 and 3). A subocular shelf extends medially from the CO3, C04, and usually the C05 the trough. A distinct ethmoid process on the ante- to form the medial margin of the orbit. Rosen and rior medial edge may be present ( + ) or absent Patterson (1969:379, Fig. 11) recently figured a ( — ) (Table 1). A ligament runs from the process subocular shelf in myctophids. Smith and Bailey to the lateral ethmoid. The anterodorsal margin is (1962:3) reported the structure present only in folded ventrally, so the anterior end of the CO1 acanthopterygian fishes, although Supino (1901: approaches a closed tube in some forms. In a num- 261, Fig. 14) briefly described and figured an ber of species, the Vn orbital organ lies on top of apparent subocular shelf in Hygophum. The medial the folded edge of the C01. In Gonichthys and process of the CO2 in Scopelarchoides nicholsi, Centrobranchus a small ossified ledge partially figured by Parr (1929:Fig. 5B), and examined in closes off the front of the C01. a cleared and stained specimen, appears to be a The CO2 (infraorbital) is shorter, but has the modified subocular shelf. Usually all of the cir- same general shape as the C01. It parallels and cumorbitals overlap one another at their margins. overlaps the maxillary and forms the ventralmost Unless the wide extension of the frontal over the portion of the orbit. The posterodorsal corner of orbit represents a fused supraorbital, no such bone the bone may be turned ventrad in some forms, was found in myctophids. and a subocular shelf is slightly developed in most Due to the great variation in number of circum- species. In three species, a suborbital photophore orbital bones in different groups of fishes, a strict lies over the CO2. In Electrona carlsbergi, but not homology has not been possible and the nomen- in Benthosema suborbitale, there is a small cup- clature is confusing. The suggestion of Weitzman shaped depression in the dorsal edge of the CO2 (1962) is followed and each bone is numbered. that contains the suborbital photophore. In Met- The nomenclature of Jollie (1954) follows in electrona sp. the suborbital photophore lies at the parenthesis. anterior end of the CO2; there is no distinct depres- The CO1 (lacrimal) is a shallow trough-shaped sion present. bone that extends from the antorbital, nasal, and The CO3 (jugal) is the largest, most variable, lateral ethmoid posteriorly to the CO2. The dorsal and most complex of the myctophid circumorbital edge of the trough constitutes the lateral margin bones. In simplest form it is T-shaped in cross of the orbit, while the ventral edge overlaps the section, with the head of the T (orbital shelf) maxillary and premaxillary. In most genera a slight forming the lateral and medial (subocular shelf) subocular shelf extends medially from the floor of portions of the orbit; the leg of the T is a broad, 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 11

TABLE 1 CHARACTERS OF THE CIRCUMORBITAL BONES (See text for explanation of characters)

1.4 Process Shelf Cone Post. Shelf Shelf Fused Shelf Split Ant. Shelf Subocular Shelf Outline Keel or Ridge

Ethmoid 04 05 05 CO3 C C CO3 CO3 CO3 CO3 C GENERA CO1 Protomyctophum + C +, A ++ Hierops +,A ++ Electrona + C A ++ Metelectrona A ++ Hygophum C, K A +, P ++ Benthosema + —,K +,A ++ Diogenichthys K A ++ Myctophum C, K A +,P +,U ++ Ctenoscopelus A ++ Symbolophorus C, K A +,U ++ Loweina A ++ Tarletonbeania A ++ Gonichthys + A ++ Cent robranchus A ++ Lobianchia + Diaphus + + + c + Notolychnus Taaningichthys ? Lam padena ++ Lampanyctodes Stenobrachius Triphoturus Parvilux A Lampanyctus A +, U + Lepidophanes —,K + +, ++ Ceratoscopelus Gym noscopelus +, A Na.solychnus +,A c Lampichthys Notoscopelus A Hintonia A Scopelopsis A triangular plate of bone that extends from the pos- variable in extent. The shelf may project anteriorly teroventral corner of the eye posteriorly towards beyond the margin of the triangular plate (A) or the end of the maxillary and the preopercle. The end at the margin of the plate ( + ) (Table 1). The lateral margin of the orbital portion of the CO3 posterodorsal end of the shelf may project beyond is solid ( — ) or split ( + ) (Table 1). A keel or the end of the plate (P) or end at the plate ( + ) flag of bone which projects posteriorly from the (Table 1). In most forms the triangular plate is lateral margin at the level of the split is present completely fused to the shelf ( + ); in some species (K), modified as a cup of bone (C), or absent either the anterior or posterior end of the plate is ( — ) (Table 1). The medial subocular shelf is not fused to the shelf (U) (Table 1). Finally, the 12 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 plane of the orbital shelf may not be perpendicular to the longitudinal axis of the fish, but may fold posteroventrally to form a concave cone of bone (Fig. 4). The cone may be absent or slightly devel- oped ( — ) or moderate to well developed ( + ) (Table 1). The C04 (postorbital) is the most posterior bone in the orbit. The orbital shelf is usually larger than the posteriorly projecting plate of bone, which is often poorly ossified. The medial subocular shelf is slightly to moderately developed ( + ) or well developed ( + +) (Table 1). The strongest devel- opment of the subocular shelf is in Tarletonbeania, Gonichthys, and Centrobranchus. The C05 (intertemporal) is slightly smaller than the C04, but has the same shape. The subocular shelf is absent in a few species of Diaphus. In other forms the degree of development is the same as, I mm or slightly less than, that on the C04. The lateral margin of the orbital shelf is either straight ( — ) or curved (C) (Table 1) in outline, and a strong ridge or keel is present ( + ) or absent ( — ) (Table 1). In some species of Diaphus the lateral orbital margin is very extensive. FIGURE 4. Left third circumorbital of Lam panyctus The C06 (supratemporal) is a small bone and regalis, 113 mm. A. Lateral view. B. Anterior view of its posterior face articulates with and partially lateral and subocular shelves. covers the sphenotic. In some forms, such as Myctophum, the C06 is completely within the The names and homologies of the posterior three orbit, while in most of the other genera, the edge bones of the teleost lower jaw are not well estab- of the lateral shelf curves out of the orbit. In some lished (Haines, 1937; Harrington, 1955; Weitzman, species of Diaphus a small keel is present on the 1962 ) . Weitzman ( 1962 : 32 ) presented evidence lateral face of the C06. The bone is often poorly for following the conventional nomenclature of ossified and occasionally lost, presumably during dentary, articular, and angular for three of the preparation of the specimen. four lower jaw bones. He followed Harrington Supino (1901) reported only four circumorbitals (1955) and others in calling the sesamoid articular in Hygophum benoiti. From his figure (Plate 18, of Starks (1916) the coronomeckelian. This term- fig. 14) he considered the CO2 and CO3 as fused inology is accepted and varies from that of Jollie into one element and apparently did not find a (1954) only in the use of coronomeckelian for his C06. All species of Hygophum examined agree prearticular. with the other myctophids in number and position of the circumorbital bones. The maxillary and premaxillary form the upper jaw and are closely joined for most of their length Mandibular Arch by strong connective tissue. The maxillary lies dor- Upper Jaw solateral to the premaxillary, except for the anteri- A striking feature among myctophids is the vari- ormost one-fifth, that swings medial to the anterior ation in jaw length in relation to the orbit. In short- portion of the premaxillary, and the most posterior jawed forms (S; Fig. 5A), the maxillary ends portion, that is medial to and supports the posterior under the posterior margin of the orbit, or projects part of the premaxillary. The maxillary does not no more than one-quarter of an eye diameter bear any teeth and is completely excluded from behind the orbit. The maxillary of long-jawed spe- the gape by the premaxillary. The maxillary is cies (L; Fig. 5B) extends one or more eye diam- overlapped laterally by the ventral portions of the eters behind the posterior margin of the orbit, first three circumorbital bones. The anterior por- while in moderate-jawed forms (M) (Table 2) the tion of the maxillary, while complex, is essentially extension is one-half the eye diameter. The changes the same in all myctophids. The anteriormost por- in shape of many skull bones appear to be corre- tion articulates on the medial face of the premaxil- lated with the change in jaw length. lary; the maxillaries do not articulate with one 1972 OSTEOLOGY AND RELATIO NSHIPS OF LANTERNFISHES 13 another on the midline. Two ligaments attach the articulates with the ethmoid just anterior to the anterior edge of the maxillary to the premaxillary, lateral tip of the vomer. A ligament runs from the one to the anteriormost tip and the other inserting anterolateral portion of the maxillary head to the just posterior to the most anterior premaxillary dorsomedial surface of the anterior part of the pre- teeth. A third ligament arises between the dorso- maxillary. The articular head of the ethmoid fits medial head and anterior tip of the maxillary and into the articular socket of the maxillary posterior attaches to the ventral side of the premaxillary of to the dorsomedial head. Opposite the socket is a the other side. These two ligaments cross in the ventrolateral projection, from which a strong liga- midline, connecting opposite maxillaries and pre- ment runs to the lateral ethmoid ventral to the maxillaries. The dorsomedial head of the maxillary nasal organ. The anterolateral margin of the socket

mm

FIGURE 5. Lateral view of left upper and lower jaw. A. A short-jawed species, Protomyctophum normani, 51 mm. B. A long-jawed species, Notoscopelus caudispinosus, 74 mm. AN—angular; AR—articular; CM—coronomeckelian; DE—dentary; MA—maxillary; PM—premaxillary; SM- supramaxillary. 14 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 articulates with the most posteromedial portion of tissue. The dorsal process of the premaxillary is the dorsal process of the premaxillary. A cartilagi- covered laterally by the ventral portion of the nasal, nous extension of the prepalatine process articu- while the ventral portions of the first three circum- lates on the dorsomedial swelling immediately orbitals cover much of the dorsolateral portion of posterior to the articular socket of the maxillary. the main shaft of the premaxillary. In a few species Rosen and Patterson (1969: Fig. 74E) have fig- the main shaft of the premaxillary bears an ured the anterior maxillary and premaxillary of a expanded dorsomedial shelf which underlies the myctophid. Behind the anterior region of the max- maxillary ( + ). In most species, the shelf is poorly illary is a relatively slim shaft. In most species a developed and the shaft itself is tilted somewhat thin, but well-developed, shelf of bone extends medially underneath the maxillary (—) (Table 2). from the ventrolateral margin of the maxillary In those forms with a well-developed shelf, it shaft and overlies the dorsal portion of the pre- usually terminates before the posterior expansion maxillary ( + ), although the shelf is absent or very of the maxillary. The shelf is present in neosco- weakly developed in a few forms ( — ) (Table 2). pelids and is much expanded anteriorly (the dis- The posterior one-fourth to one-tenth of the max- tal premaxillary process of Greenwood et al., illary is either greatly ( + ), moderately (M), or 1966:366, Fig. 3). The anterior tip of the pre- slightly ( — ) (Table 2) expanded ventrally. A small maxillary has a dorsal process which articulates dorsal expansion on the posterior tip of the maxil- with the rostral cartilage. The medial edges of the lary may be absent ( — ), short (S), or long (L) processes of either side articulate loosely in the (Table 2). midline. The homologies of the premaxillary dorsal In some genera a small supramaxillary is present process of myctophids with what have been called ( + ) (Table 2), dorsal and medial to the posterior the articular and ascending processes in other area of the maxillary. It is a very thin bone and teleosts is uncertain (Greenwood et al., 1966:367- appears dermal in origin. The bone is L-shaped; 369) ; the dorsal process in myctophids may rep- the long leg is parallel and dorsal to the maxillary, resent a fusion of the two processes. Weitzman the short leg perpendicular and medial. The short (1967a:525) suggested that the ascending process leg terminates in a ligament which runs from the could have been independently derived a number dorsal tip of the articular to the medial side of the of times in teleosts. Although the dorsal process in maxillary and premaxillary. The bone approximates the various myctophid genera displays slight differ- the supramaxillary of Scopelarchoides nicholsi ences in shape, no major distinctions were noted. (Parr, 1929: Fig. 5C) in size and position. In The internal surface of the process is usually Hintonia, the supramaxillary is reduced to a small slightly concave and the posterior medial edge is bone, somewhat trapezoidal in shape (found in one thickened for articulation with the maxillary. The specimen) or is absent (one specimen). One or premaxillary-maxillary ligaments have been de- more scales from the series dorsal or lateral to the scribed above. The premaxillary-palatine ligament, posterior maxillary may remain in cleared and characteristic of neoscopelids (Greenwood et al., stained specimens; these have clearly defined 1966:366-367, Fig. 3B), is absent in myctophids. growth rings which the supramaxillaries lack. The Lower Jaw supramaxillary either represents the degenerate posterior supramaxillary found in some salmonoid The articular comprises approximately the pos- and other myctophoid fishes or is a new element. terior third of the lower jaw. The area of Meckel's The supramaxillary of neoscopelids is long, slender, cartilage divides the articular into dorsal and ven- and lies dorsal and parallel to the posterior tral halves. The posterior projection of the ventral maxillary. half, the retro-articular process, supports the artic- The premaxillary is the tooth-bearing bone of ulation of the quadrate. A dorsal articular process the upper jaw and effectively excludes the maxillary projects just anterior to the quadrate articulation. from the entire gape. In those forms where the It is medial to the expanded portion of the max- greatly expanded posterior portion of the maxillary illary, and bound to it by ligaments and connective extends ventral to the premaxillary, the expansion tissue. The posterior area of the dorsal process is is behind the rictus and lacks teeth. A variety of irregularly thickened and varies in shape among tooth patterns are found in myctophids; the pre- different genera. The dentigerous portion of the maxillary teeth will be discussed below in conjunc- dentary ends just anterior to the process, and the tion with the dentary teeth. The posterior portion two are connected by a short ligament, a branch of of the premaxillary is lateral to the maxillary and which runs to the medial side of the posterior part closely bound to it by ligaments and connective of the maxillary. Here the dorsal margin of the the ventralborderoflowerjawtoarea dentary overlap,andthenascends totheanterior tip. Onthemedialside,posterior tothecorono- tary. Theventralmarginofthearticularcomprises a shortdistance. GENERA meckelian, Meckerscartilage appearscalcifiedfor articular anglesventrallytoananteriorpoint.The Scopelopsis is overlappedby,theposteriormarginofden- Ceratoscopelus anterior portionofthearticularliesmedialto,and Gymnoscopelus Lampichthys Lepidophanes Lampanyctus Stenobrachius Symbolophorus Hintonia Nasolychnus Centrobranchus Gonichthys Taaningichthys Lobianchia Lam panyctodes Notoscopelus Diaphus Ctenoscopelus Tarletonbeania Triphoturus Lam padena Loweina Hygophum Hierops Notolychnus Parvilux Myctophum Ben thosema 1972 Electrona Protomyctophum Metelectrona Diogenichthys

< x

S, S, L M,L OSTEOLOGY ANDRELATIONSHIPSOFLANTERNFISHES

Maxillary Shelf CHARACTERS OFTHEUPPERANDLOWERJAW (See textforexplanationofcharacters)

Post. Max. Vent. Exp. S, L, S L, S S —

Post. Max.Dors. Exp. TABLE 2 shaped indifferentgeneraandisassociatedwith the anteroventraltipof interopercletothe pansion ofMeckel'scartilage. Aligamentattaches what appearstobeanossifiedareaonaventralex- angular. retro-articular process.Theangularisirregularly face ofthearticular,immediatelyanteriorto

The coronomeckelianisasmall bonethatlies The angularisasmallboneonthemedialsur- Supramaxillary - - _

PremaxillaryShelf BONES - M, H - F, L - - - M

E Ant.Premax. Teeth

- - _

Post.Premax. Teeth L, W M

E Ant.Dentary Teeth M, H m, E m, E - -

E E Post.Dentary Teeth 15 16 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13 approximately in the middle of the articular on the teeth appear to be of two parts: a short base or medial side. It is the point of attachment for the pedicle, and a longer crown. The teeth are depres- pars mandibulares of the adductor mandibulae sible toward the oral cavity and bend at the line muscle (Jollie, 1954:58). Supino (1901) did not separating the base and the crown. In a number of report a distinct angular or coronomeckelian species the teeth increase in size from labial to oral (coronoid) in Hygophum benoiti; however, I have row, while in others the change is from anterior to found both elements in all myctophids examined. posterior. The rows are often irregular and the The dentary, largest bone of the lower jaw, is teeth may best be described as occurring in bands. complex in shape, with a dorsal tooth-bearing plate, Usually the approximate number of rows is four a midlateral ridge, and a ventral sheet. The pos- to six. Apparently beyond a certain size, the num- terior margin of the dentary is irregularly curved ber of tooth rows does not increase with age but as it overlaps the anterior margin of the articular the size of the individual teeth do. There may be a on the lateral side. The anterior portion of the slight reduction in band width, or in the number dentary dorsal to the lateral ridge is a closed tube of tooth rows, at the anterior and posterior ends containing the mandibular nerve. The medial wall of the dentary and premaxillary. At the posterior of the tube ends about half the length of the den- end of the dentary the reduction is greatest and a tary, and the most anterior tip of the articular single row may result. In Taaningichthys, Lampa- usually lies just inside the open end of the tube. dena, one species of Lepidophanes, and Notoscope- The anterior portion of the dentary curves medi- lus, the anteriormost dentigerous surface of the ally to meet its opposite from the other side; they premaxillary is slightly expanded; in all but the last are closely bound together at the midline. The genus, enlarged teeth are borne on the expanded dentary terminates anteriorly in a slight dorsal pro- area. jection. The anterior region of the ventral sheet One modification of the generalized dentition is is irregularly sculptured; often a small projection, the development of large, broad-based, strongly from which a ligament arises, is present. As Gos- hooked teeth (H), found in a number of genera. line et al. (1966:6) pointed out, the mandibular The teeth are often on the most posterior portion canal of the head sensory system runs along the of the dentary, invariably in a single row, with lateral side of the ventral sheet of the dentary and other rows of smaller conical teeth present later- is covered externally only by skin. At the anterior ally or absent. The hooked teeth usually curve for- end of the dentary, the canal enters a very short ward, but when they occur in the anterior part of tube, about one-half as long in myctophids as that the jaws, they curve posteriorly. They are some- figured by Gosline et al. (1966: Fig. 4C) for Neo- what depressible orally. In some forms the teeth scopelus. The dentigerous portion extends almost apparently increase in number with age; a 108 mm to the symphysis; the most posterior dentary teeth specimen of Lam padena speculigera has a row of are behind the rictus and lie medial to the posterior 15 hooked teeth in the posterior dentary, while part of the maxillary. The posterodorsal region of seven teeth were found in a 22 mm specimen. the dentary is slightly expanded dorsally behind or However, in Triphoturus mexicanus six to seven lateral to the last teeth in Notolychnus, some Dia- teeth were found both in 20 mm and 50 mm speci- phus, Lam padena, Triphoturus, and Hintonia. The mens. They may be functionally more important greatest dorsal expansion is found in Lampanyctus in the smaller specimens of T. mexicanus, where and Parvilux. they are the largest teeth on the jaw; in the larger Although the shapes of the lower jaw bones are examples the conical teeth have increased in size somewhat different in various myctophid genera, and number to surround completely the hooked the basic plan of the lower jaw is the same in all teeth and equal them in size. In a number of forms myctophids. In short-jawed forms the dentary is modified hooked teeth occur (M). These teeth are deeper in relation to its length than in long-jawed not as large and the curvature is not nearly as pro- species; no lower jaw characteristics are distinctive nounced as in the hooked teeth; however, the mod- enough to provide unambiguous character states. ified hooked teeth have broad bases and occur in Conversely, the dentary and premaxillary denti- a single row, where they usually number from five tion displays some striking modifications in lan- to nine. They have been figured by Bolin (1939: ternfishes. Typically, the ventral surface of the 124) and Nafpaktitis (1966:414). Although the premaxillary and the dorsal surface of the dentary, modified teeth usually occur on the posterior part from symphyseal to posterior end, are covered by of the premaxillary and dentary, they are occa- a number of rows of small, conical teeth, with the sionally found on the front of the jaws. In the tips curved slightly anteriorly or medially. The expanded anterior dentigerous areas of the pre- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 17 maxilla of Taaningichthys, Lampadena, and Lepi- TABLE 3 dophanes the enlarged teeth are of the modified CHARACTERS OF THE PALATINE ARCH hooked type. A few genera have small modified (See text for explanation of characters) teeth, usually smaller than the conical teeth, but still in a single row and with slightly broadened bases (m). A few species have greatly enlarged Strut conical teeth (E), usually in the inner tooth row of the premaxillary or dentary. A number of tooth specializations are found in the genus Diogenich- thys. In addition to a series of strongly hooked teeth on the posterior portion of the dentary, an Quadrate Foramen Metapterygoid outer row of closely-set short teeth which are GENERA Palatine Tooth Rows wider than long is present on the anterior part of Protomyctophum S V 1-3 the dentary (W). Teeth of the inner row are elon- Hierops S V 1-2 gate, set further apart, and are somewhat flattened Electrona S V 1-3 (F). The teeth on the anterior two-thirds of the Metelectrona S V 1 premaxillary of D. atlanticus and D. panurgus are Hygophum S V 1-4 in a single row and are flattened, lanceolate and Ben thosema S V 1-6 closely set with small projections on their edges Diogenichthys S V 1-3 (1) (Table 2), as described and figured by Bolin Myctophum S V 1-7 (1939:119) for D. 1aternatus. In my specimens of Ctenoscopelus S V 6-7 D. laternatus, the premaxillary teeth are similar to Symbolophorus S, L V 1-7 the inner row of dentary teeth found in all species Loweina S V 1 of the genus. In the neoscopelids, the teeth of Tarletonbeania S V 2-3 Neoscopelus and Scopelengys agree with the gen- Gonichthys 2-3 eralized myctophid condition, although the ante- S V Cent robranchus 2-6 rior and inner teeth tend to be the largest. In S D Lob ianchia D Solivomer, the jaws are covered with a band of S, L 4-7 minute teeth. Diaphus S, L V, D 1-7 Notolychnus S D 1 Palatine Arch Taaningichthys S, L D 1-2 Lam padena L D 1-2 The quadrate is a triangular bone that lies at Lam panyctodes S D 1-3 the posterior end of the jaws (Fig. 6). The base of Stenobrachius L D 3-5 the triangle is dorsal; the posterior one-third to Triphoturus S D 1-3 two-thirds of the dorsal edge are slightly separated Parvilux S D 3-4 from the ventral margin of the metapterygoid by Lampanyctus S, L D 2-8 connective tissue. The anterior one-third to two- Lepidophanes S D 3-5 thirds of the dorsal edge appear fused to the poste- Ceratoscopelus S, L D 1-3 rior portion of the ectopterygoid. The posterior Gymnoscopelus S, L D 1-5 margin of the quadrate is closely bound to the Nasolychnus L D 1-4 symplectic. A short distance below the dorsal mar- Lampichthys L D 3-4 gin, the lateral face of the posterior edge of the Notoscopelus S, L D 5-6 quadrate covers the symplectic and forms a trough Hintonia L D 1-2 in which the symplectic lies. The ventral tip of the Scopelopsis L D 2-3 quadrate forms the articulation for the lower jaw. An anteroventral projection overlies the articular of the lower jaw laterally, and a small ventral pro- in this area of the skull; the quadrate is very heav- jection lies medial to the articular. A foramen in ily ossified in the ventral portion, where it rests on the base of the quadrate, between the two projec- the articular. tions, varies in size from small (S) to medium or The metapterygoid is a flattened bone lying large (L) (Table 3). between the hyomandibula, quadrate, and mesop- Supino (1901) stated that the quadrate is so terygoid. A posterolateral strut, which articulates weakly ossified that only with sectioning did the with the main shaft of the hyomandibula, projects bony lamellae become evident. On the contrary, I from and reinforces the posterior margin of the find the quadrate as well ossified as any other bone metapterygoid. The posterolateral strut either pro- 18 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No.13 jects dorsally from the main body of the bone (D) gin of the ectopterygoid and usually by the poste- or does not extend above the dorsal margin of the rior margin of the mesopterygoid. main body (V) (Table 3). When an orbital proc- The ectopterygoid is a long, flattened bone in ess of the hyomandibula is present, it is medial to the lateral roof of the mouth that forms the ven- the posterior portion of the metapterygoid. Ven- trolateral margin of the palate between the palatine trally the metapterygoid is slightly separated from and the quadrate. Posteriorly the ectopterygoid the dorsal margin of the quadrate. The anterior slightly overlaps portions of the quadrate and margin is slightly overlapped by the posterior mar- metapterygoid. A posterior leg bends ventrally

FIGURE 6. Medial view, modified perspective (bones were moved during drawing), of left pala- tine arch and symplectic. A. A short-jawed species, Electrona antarctica, 84 mm. B. A long- jawed species, Lampichthys procerus, 66 mm. EC—ectopterygoid; MS—mesopterygoid; MT- metapterygoid; PA—palatine; QU—quadrate; SY—symplectic. 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 19 along the anterior margin of the quadrate. Ante- Notolychnus the mesopterygoid does not extend riorly the ectopterygoid narrows and lies between forward much beyond the posterior margin of the the palatine and mesopterygoid. Its anterior end palatine and the post-palatine process and dorsal lies one-half to four-fifths of the way up the pala- wing are unossified. A small ligament joins the tine. Rarely the ectopterygoid bears minute, widely lateral face of the dorsal wing, at its connection separated teeth. with the main body of the palatine, to the dorso- The mesopterygoid is a thin, slightly curved bone lateral edge of the maxillary, immediately behind that is the main, medial, ossified support for the the posterior swelling of the articular socket. The eyeball. Along its dorsal margin the mesopterygoid postpalatine process appears to articulate through is attached to the parasphenoid by strong connec- cartilage with the medial portion of the lateral tive tissue. The general shape of the mesopterygoid ethmoid. The prepalatine process, which has a is correlated with the length of the jaws. In short- large cap of cartilage, articulates through cartilage jawed forms it is about twice as long as wide. with a lateral portion of the lateral ethmoid. A Posteriorly it usually overlaps the metapterygoid, ligament connects the ventral projection and the and most of the ventral margin is bordered by the anterior portion of the prepalatine process to the ectopterygoid. Anteroventrally the mesopterygoid lateral tip of the vomer. The ventrolateral portion usually overlaps a dorsal wing of the anterior por- of the prepalatine process articulates with the tion of the palatine. The oral surface invariably maxillary swelling posterior to the articular socket. bears teeth, but there is wide variation in the devel- Gosline et al. (1966) discussed the maxillary- opment of the dentigerous area: more than nine- palatine articulation in salmoniform and myctophi- tenths of the oral surface may be covered with form fishes. The usual myctophiform condition, small, closely-set teeth; the teeth may be restricted typified by Chlorophthalmus, in which the palatine to one small patch in about the middle of the has a laterally directed anterior process for the bone; or there may be one row of widely spaced maxillary articulation (Regan, 1911:121; Gosline teeth in the middle of the mesopterygoid. Most et al., 1966: Fig. 1C) is not found in myctophids. myctophids have approximately three-quarters of The prepalatine process, while capped by cartilage, the oral surface toothed. The variation described gives only a very slight indication of lateral direc- is probably correlated with differences in ecology tion when viewed from above. and feeding habits of the species involved; almost In most myctophids, the entire ventromedial as much variation exists between the species within surface of the palatine bears teeth. In some species some individual genera as exists within the entire of Protomyctophum, Hierops, Electrona, Metelec- family. trona, Diogenichthys, and Hygophum, the posterior The palatine is an elongate bone with a slightly one-half to one-fifth of the palatine may lack teeth. flattened posterior region and a complex anterior The palatine teeth are usually in a band of one to portion which articulates with or is joined by liga- eight irregular rows (Table 3). If the band is wide ments to the vomer, lateral ethmoid, maxillary, with many rows, the teeth are usually small and and mesopterygoid. No premaxillary-palatine liga- closely set. If the band is of one or two rows, the ment was found in the myctophids examined. The teeth are usually much larger and widely spaced; palatine lies medial and just dorsal to the maxil- the largest palatine teeth are found in some species lary; its ventral margin is joined to the maxillary of Electrona, Metelectrona, and Loweina. Palatine by connective tissue. The dorsal margin of the teeth usually increase slightly in size from medial palatine is bordered by the ecto- and mesoptery- to lateral and from posterior to anterior. The dor- goids. The anterior region is generally made up of sal wing of the palatine and the oral surface of three parts: a dorsal, slightly posterior, postpala- the pre- and postpalatine processes never bear tine process; a prepalatine process that is the most teeth, while the ventral anterior process almost anterior portion of the palatine; and a small ven- always is dentigerous. tromedial process under the prepalatine that appears to be a continuation of the main body of Hyoid Arch the palatine. In a number of forms the ventral The hyomandibula and symplectic, although process is developed into a definite spike. The derived from the hyoid arch, have become in posi- region posterior to the postpalatine process is ossi- tion and function a portion of the superficial skull fied dorsal to the main body of the bone, and may bones and an integral part of the suspensorium for be termed the dorsal wing of the palatine. The the lower jaw. The rest of the hyoid skeleton is posterior portion of the dorsal wing usually over- medial to the jaws and superficial skull bones. laps the anterior region of the mesopterygoid. In Jollie (1954) discussed the homology of the 20 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. I3 hyomandibula in various fish groups and consid- ered the hyomandibula homologous to the epihyal. He used the name epihyal externus for the teleost hyomandibula. However, Jollie used the name hyo- mandibula in his more general work (1962), and this well-known name is retained in the present work. Although the hyomandibula is apparently homologous to the epihyal (Goodrich, 1930:405; Jollie, 1954, 1962), the terminology proposed by Jollie, ceratohyal posterior and anterior, is confus- ing; the conventional terminology of epihyal and ceratohyal (Harrington, 1955; McAllister, 1968; Weitzman, 1962) is retained herein. When present, FIGURE 7. Lateral view of left hyomandibula. A. A the basihyal of modern teleosts is a single median short-jawed species, Myctophum phengodes, 57 mm. B. bone of endochondral origin, which is often over- A long-jawed species, Lam panyctus ingens, 135 mm. lain by a usually dentigerous plate of dermal ori- gin. These two elements have been variously called the entoglossal (Jollie, 1962), glossohyal (Starks, mandibular head is slightly wider than the first. 1901; Phillips, 1942), and copula I (Harrington, The main trunk of the hyomandibular nerve runs 1955). In this work the endochondral element is through part of the hyomandibular shaft and ante- termed the basihyal (Harrington, 1955; Nelson, rior head (Jollie, 1954). The canal for this nerve 1967, 1969) and the dermal element the lingual opens about halfway up the anterior head on the plate (Norden, 1961). medial side. A foramen is present just dorsal to the medial opening, either through the anterior The hyomandibula is an elongate bone that sus- head (H), or through the ossification between pends the jaws from the skull. Dorsally two heads heads one and two (B) (Table 4). On the postero- articulate with the cranium, an anterior head on lateral face of the hyomandibular shaft, lateral to the sphenotic and a posterior head on the pterotic. and about the level of the opercular head, is a Posteriorly about one-third of the way down the process for the articulation of the preopercle. The shaft, a third head articulates with the opercle. All process is weakly developed (W), moderately heads are capped with cartilage. Along the postero- developed (M), or strongly developed (S) (Table face of the shaft lies the preopercle. The lateral 4). It appears to increase in relative size in larger posterior edge of the metapterygoid abuts against specimens. and partially fuses with the anterior face of the The space between heads one and two is always ventral half of the hyomandibular shaft. Ventrally ossified. The space between the second and third the shaft is connected to the dorsal end of the heads can be completely or almost completely ossi: symplectic by cartilage. The interhyal articulates fled ( + ), moderately ossified (M), or have little on the medial face of this connection. or no ossification ( — ) (Table 4). In those forms Much of the variation of the hyomandibula in with no ossification between the heads, a small to myctophids is apparently associated with the moderate process may be present ( + ) or absent change in length of the upper and lower jaws. In ( — ) (Table 4) on the dorsal side of the opercular short-jawed species the hyomandibula is a straight head. Associated with the shift in position of the vertical bone with only the anterior head curving hyomandibula with increasing jaw length is the slightly anterodorsally (Fig. 7A). In long-jawed widening of the angle between heads two and species the bone retains its basic shape but changes three. The angle is greatest, approaching 180°, in position relative to the cranium (Fig. 7B). Notolychnus and Triphoturus. Apparently associated with the change in posi- The symplectic is an elongate, slightly flattened tion is the appearance of a well-developed orbital bone lying at the posterior edge of the quadrate process from the anterior face of the dorsal half (Fig. 6). Its dorsal margin articulates through cart- of the shaft and anterior head. The process can be ilage with the hyomandibula and interhyal. The absent to slightly developed ( — ), or moderately dorsal margin of the symplectic may be on the to fully developed ( + ) (Table 4), as a broad, same level with the dorsal margin of the quadrate triangular plate that supports part of the postero- ( = ), or it may extend dorsal (D) or ventral (V) lateral roof of the mouth. In most species it is thin to it (Table 4). The ventral portion of the symplec- and may be very weakly ossified in some species tic is tightly wedged into the posterior trough of of Diaphus. In most myctophids the second hyo- the quadrate. 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 21

TABLE 4 CHARACTERS OF THE HYOID ARCH (See text for explanation of characters) 3

cn Head Proc. and 2 Margin Urohyal Urohyal Orbital Process 1.4 Heads Posterior Hyom. Symplectic Anterior GENERA Hyom. Hyom. Preoper. Hyom. Opercular Protomyctophum — H W D, = 0+4-6 8-10 Hierops — H W =, V 0+5-6 9-10 Electrona — H W, M D, = 0-1+3-4 7-8 +, S —, A Metelectrona — H W 0+4 8 A Hygophum — H M D, = 0-1+4-5 9 P, Benthosema — H M M D, 0+4 8 S, Diogenichthys + H W, M 0+3 7 A Myctophum + H M, S + =, V 0-2+3-5 8-9 S, - —, A Ctenoscopelus — H M 1 +4 9 + A Symbolophorus + H S M, + D, = 1 +4 9 Lowe m a + H S V 2+3 9 A Tarletonbeania + H S V 1+3 8 A Gonichthys + H M 0+5 9 A Centrobranchus + H S V 0-1+2-4 7-8 S, - A Lobianchia + H S V 1+4 9 + P, Diaphus + H, B M, S M =, V 1-2+3-4 8-9 +, S Notolychnus + B S V 1-2+4 9-10 Taaningichthys + B M V 0-1+3-4 8-9 + S Lampadena + B S V 1 +4 9 Lam panyctodes + B S V 3+4 11 Stenobrachius + B M, S + V 2+3-4 9-10 Triphoturus + B M V 1-3+4 10-11 Parvilux + B M V 2-3+4 10-11 Lampanyctus + B M =, V 2-3+2-4 8-11 Lepidophanes + H S + 1+4 9 +, — Ceratoscopelus + H S D, = 1-2+3-4 9 +, S Gymnoscopelus + H, B M, S + V 2+4 10 +, S P, — Nasolychnus + B M, S + V 2-3+4 10-11 +, S —, A Lampichthys + H S V 1+4 9 Notoscopelus + H S V 2+4 10 Hintonia + B S V 1-2+3 9 A Scopelopsis + H S V 2+4 10

Supino (1901:264) reported the presence of The interhyal articulates on the medial face of calcified cartilage in the middle of the symplectic the symplectic connection. It is a slender bone and in the dorsal portion of the hyomandibula. connected by a ligament to the posterior end of Alizarin Red stains calcified cartilage, as well as the epihyal. Supino (1901) reported the interhyal bone (Smith, 1945); in all specimens examined to be completely cartilaginous in Hygophum beno- by me, the internal cartilage of these bones is not iti. In all myctophids examined in this study, the stained and gives no indication of being calcified. interhyal is well ossified. 22 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

The epihyal is a short, flattened bone that articu- ment from the anterior of the first hypobranchial. lates anteriorly through cartilage to the ceratohyal. Two strong ligaments also extend from the anterior Posteriorly it tapers slightly and is joined to the head of the urohyal to the anteroventral portion anterior margin of the interhyal. of each hypohyal. A few tooth patches are present The ceratohyal is the largest bone in the func- on the medial face of the hypohyal in some species. tional hyoid arch. It articulates anteriorly by car- The branchiostegal rays articulate with the epi- tilage to the hypohyal and, like the epihyal and hyal, ceratohyal, usually the hypohyal, and the hypohyal, is much flattened laterally. Just poster- cartilaginous area between the hypohyal and cera- ior to the middle, the bone increases in depth. A tohyal. McAllister (1968) stated that the basic foramen in the middle of the ceratohyal has been acanthopterygian number and position of branchi- considered a character of beryciform fishes by ostegals is X rays inserted on the ventral or internal McAllister (1968:6) and a primitive character for face of the hyoid arch and four rays inserted on the most lower teleosts by Rosen and Patterson external or lateral face of the arch. Myctophids fall (1969:408). A perforate ceratohyal is here into this pattern, with the last two rays inserted on reported in a myctophid, although the latter the lateral face of the epihyal and the next two authors (1969:453) suggest that the only advanced inserted on the posterolateral face of the cerato- character uniting all myctophiform fishes is the hyal. Except for one side of one specimen of shallowing and loss of the fenestra in the cerato- Hintonia candens with five external rays, this pat- hyal. In almost all myctophid specimens exam- tern is constant for all specimens examined. The ined, the central area of the ceratohyal is not solid, variation is thus in the number of medial or inter- but unevenly ossified. In adults of two species, nal rays which articulate on the hypohyal and Notolychnus valdiviae and Triphoturus mexicanus, ceratohyal. Often one ray articulates with the car- a foramen is present in the middle of the cerato- tilaginous area between the two bones; these are hyal (Fig. 9). In Notolychnus, (adults 20-25 mm) arbitrarily shown as articulating on the ceratohyal the foramen is large, about one-half the depth of (Table 4). The numbers in the table refer to the the ceratohyal. In T. mexicanus the foramen rays on the hypohyal plus those on the medial side decreases in size with increasing specimen size. In of the ceratohyal; the posterior four rays which 40-50 mm adults, the foramen is either small or articulate laterally must be added to obtain the total covered over by uneven ossification, while in speci- ray count, which ranges from seven to 11 for the mens of 20-30 mm the size of the foramen approx- family (Table 4). imates one-quarter the depth of the ceratohyal. Supino (1901) reported nine branchiostegal rays No other species examined, of any size, has a fora- in Hygophum benoiti, and figured the posterior men. The fact that Notolychnus and Triphoturus four rays as articulating on the epihyal (Plate 18, are two myctophid genera with the most poorly Fig. 21). While there are often nine branchiostegal ossified bones may be correlated with the presence rays in lanternfishes (and in all species of Hygo- of the foramen, although a specimen of T. nigres- phum examined in this study), never more than cens lacked the foramen. Of the three neoscopelid two rays articulate on the epihyal in any mycto- species examined, a large (122 mm) specimen of phid. Such a character would indicate that Supino Scopelengys tristis had a well-developed foramen, was not working on a myctophid at all, but on while Neoscopelus macrolepidotus and Solivomer some other form. However, the characters figured arenidens had the unevenly ossified central area in his Plate 18, Figs. 14 and 15, particularly the characteristic of most adult myctophid species. apparent subocular shelf on the posterior circum- The hypohyal is a short, laterally flattened bone orbitals and the hyomandibula with two dorsal that appears to be composed of two fused elements, heads, are indicative of a lanternfish. In addition, a thin dorsal unit and a main ventral portion. A the short jaw and widely expanded posterior max- suture line is visible in many specimens. Jollie illary are characteristic of Hygophum, as well as (1954) stated that the ossified portions do not cor- some other genera of myctophids. All of the other respond to the dorsal and ventral cartilaginous differences noted previously between the descrip- cores of the hypohyal in Stenobrachius leucopsarus. tion by Supino and that of the present work can The hypohyals of each side meet in the midline be attributed to his failure to find a suitable stain and are joined by connective tissue. The dorsal for bone and cartilage, and therefore his difficulty portions articulate with each other and with the in differentiating between the two. It may be noted median first basibranchial. Ascending processes in this context, that the "orbitosphenoid" of Supino arise from the articulation point of each dorsal (Plate 18, Fig. 14) is in fact extremely tough portion and serve for the insertion of a strong liga- connective tissue forming the interorbital septum 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNF1SHES 23 between the parasphenoid and frontal. In general rodorsally to posteroventrally (Fig. 8). Dorsally form and in most details, the figures and descrip- the preopercle lies against the preopercular proc- tions of Supino fit that of myctophids, and I take ess of the hyomandibula. Below the hyomandibula the posterior articulation of the branchiostegal it is intimately connected to the posterior edge of rays in his Fig. 21 to be an error of illustration. the quadrate that completely encases the ventral No ossified basihyal is evident in any myctophid three-fourths of the symplectic. At the level of the examined, although a very small ossification in the cartilaginous juncture of the hyomandibula and center of the basihyal cartilage is present in some symplectic, a small shelf projects anteriorly from specimens of Tarletonbeania and Myctophum. A the main axis of the preopercle. The shelf probably very small cartilage anterior to the hypohyals rep- serves to strengthen the area of the interhyal artic- resents the remains of the basihyal. Supino (1901) ulation. A strong keel projects laterally from the reported a thin bony layer over the basihyal (ento- preopercle for almost its entire length. Posteriorly glossal) cartilage in Hygophum benoiti, a species a weakly ossified sheet of bone arises from the that has not been examined in the present study. main axis and partially overlies the other oper- In the three neoscopelids examined, an ossified cular bones. The sheet is often divided into dorsal basihyal is invariably present. It is most strongly and ventral sections at approximately the level of ossified, although small, in Solivomer, moderately the hyomandibula-symplectic articulation. The ven- ossified in Neoscopelus, and only the posterior tip tral portion is more strongly ossified; on its median between the hypohyals is ossified in Scopelengys. face is an area of strong ossification which strength- No lingual plate is present in either the myctophids ens the sheet in the form of a ridge or keel. A or the neoscopelids examined. branch of the adductor mandibularae muscle (Jol- The urohyal is a single median element ventral lie, 1954) runs from this keel over the quadrate to the basibranchials. It is a dermal bone, and not to the lower jaw. Both the muscle and keel appear truly a part of the hypobranchial skeleton (Nor- to be more highly developed in long-jawed forms. den, 1961; Ridewood, 1904:76) although it is In some myctophid genera a thin flag of bone pro- intimately associated with the hypobranchial ele- jects posteriorly from the dorsal tip of the pre- ments. The urohyal is composed of an anterior, opercle. This flag apparently originates as a free thin rod, which usually begins at the level of the scale bone, as is found in some species. The flag posterior end of the first basibranchial, and a later- may be absent ( — ), free ( + ), or fused to the ally flattened posterior wing, which extends approx- preopercular tip (F) (Table 5). It is often very imately to the level of the posterior ends of the weakly ossified and may be homologous to the third hypobranchials. The dorsal margin of the suprapreopercle found in some salmonids (Nor- posterior wing is strengthened by a continuation den, 1961:731). of the anterior rod. The anterior tips of the third hypohyals articulate with the dorsal region of the urohyal wing. In many species the anterior rod is bifurcated for up to one-third of its length and has two well-developed heads ( + ), each of which has a ligament to the anterior areas of the hypohyals. In a few species there is no indication of a split ( — ), while in others the rod is slightly split (S) (Table 4). The ventral expansion of the urohyal wing begins either far before the anterior ends of the second hypobranchials (A), posterior to this point (P), or approximately at the same level ( — ) (Table 4). An anterior origin of the urohyal wing indicates a much shortened anterior rod. I did not find abundant cartilage in the urohyal (basibran- chiostegal ), as reported by Supino (1901).

Opercular Apparatus The preopercle is an elongate, many-faceted bone, and its main axis is immediately posterior to FIGURE 8. Lateral view of left opercular bones of the hyomandibula and quadrate. Slightly lunate in Lampanyctus jordani, 104 mm. IO—Interopercle; OP- shape, the preopercle runs dorsoventrally or ante- opercle; PO—preopercle; SO—subopercle. 24 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13

The opercle of myctophids, the largest of the Jollie (1954) called the first three basibranchials opercular series, is like a very large scale. It articu- and the plate the copula, a name that has previously lates with the opercular head of the hyomandibula, been used for several parts of the hypobranchial is partially overlain by the dorsal portion of the skeleton. The terminology of Nelson (1967, 1969) posterior sheet of the preopercle, and either slightly which differentiates the individual basibranchials overlaps the subopercle or is fused to its dorsal from the dorsal, dentigerous basibranchial plate, is margin. The opercle may be weakly or heavily adopted for the present work. ossified. It is always strengthened by at least one The first branchial arch from anteroventral to ridge on the medial face, running posteriorly from posterodorsal consists of a median basibranchial the hyomandibular articulation. In all but a very and paired hypo-, cerato-, epi-, and pharyngobran- few forms a ridge from the articulation runs ven- chials which articulate with each other through trally, parallel to the anterior edge of the opercle. cartilaginous areas. The first basibranchial is prob- In most short-jawed forms a dorsal ridge runs ably composed of the fused basibranchials of each parallel to, or forms the anterior edge of, the side although no suture is evident. It articulates opercle dorsal to the articulation point. In many anteriorly with the hypohyals and posteriorly with long-jawed groups a ridge runs posteroventrally the anterior end of the second basibranchial by an from near the origin of the posterior ridge to the area of intervening cartilage. The anterior head of posteroventral corner of the opercle. The postero- each of the first hypobranchials is inserted on the dorsal margin of the opercle may be smooth or lateral face of this cartilaginous area between the very weakly dentate (S), or moderately to strongly first two basibranchials. The first basibranchial ap- dentate (D) (Table 5). Rosen and Patterson pears to consist of two parts, a thin dorsal portion (1969:448, Fig. 64) figured a strongly dentate and the main ventral body. The posterior one-half opercle of a myctophid they identified as Diaphus to one-third is overlain by the anterior portion of theta; although such strong spines are found in a the basibranchial plate. In some species, such as number of species of Myctophum, I found only Stenobrachius leucopsarus, the anterior dorsal por- weak spines in some species of Diaphus. The tion of the basibranchial plate is fused so strongly cleared and stained specimens of Diaphus theta with the dorsal portion of the first basibranchial examined in this study all possessed smooth that no suture lines are evident. In most mycto- opercles. phids, however, the two bones can be separated. subopercle lies between and is firmly The thin The hypo-, cerato-, and epibranchials of the first opercle interopercle; it is attached to the and arch bear gill rakers on the lateral faces and gill slightly overlapped by each.' The subopercle forms teeth or patches of teeth on the medial faces. The the posteroventral corner of the opercular appara- number of gill rakers varies greatly within genera. tus in short-jawed forms and the posterior border In Centrobranchus the gill rakers are replaced by in long-jawed forms. patches of small teeth. Each of the three bones is The sheetlike interopercle lies between the sub- long, thin, and slightly flattened laterally. The cera- opercle and the ventral section of the preopercle. tobranchial is the longest, with both the hypo- and Its anterior edge is strengthened by a ridge that epibranchials about one-third to one-half as long. terminates slightly before the ventral margin. A Patches of small teeth are on the dorsal surface of ligament arises at this point and connects the inter- the bones between the gill rakers, and the gill rakers opercle with the angular of the lower jaw. themselves are covered with minute teeth. A head The opercular bones display various changes in on the posterodorsal surface of the epibranchial shape which may be partially correlated with jaw articulates by cartilage with the posterodorsal head length. It has not been possible to categorize the of the second pharyngobranchial. The shape of the shapes for purposes of comparison. Portions of the epibranchial head varies in different genera, from opercle, subopercle, and interopercle may be com- short and broad to long and thin. The first pha- pletely unossified. ryngobranchial is a very short, thin bone that artic- ulates with the dorsolateral expansion of the Branchial Arches parasphenoid, near the prootic. The pharyngo- In myctophids, elements of five branchial arches branchial extends vertically from the anterior head are present (Fig. 9). They are medial to the func- of the first epibranchial. In most species a single tional hyoid arch and form the floor and posterior patch of teeth is present on the anterior face of portion of the oral cavity. the pharyngobranchial near its ventral base; how- The basibranchials are overlain by and some- ever, the number of patches varies from none to times fuse to a median, dermal, dentigerous plate. six within the family (Table 5). 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 25

The three main bones of the second branchial articulate at the cartilaginous area between the arch, the hypo-, cerato-, and epibranchials, are second and third basibranchials. The lateral face essentially the same shape as those of the first arch, of the cerato- and epibranchials bear short gill although smaller. The second basibranchial is a rakers near their cartilaginous articulation, while median bone that articulates with the first and third the remaining lateral faces bear gill teeth, as do the basibranchials through cartilage. Both the second medial faces. The anterodorsal end of the epibran- and third basibranchials may bear tooth patches chial ends in two closely associated heads, one of or single, relatively large teeth on their lateral faces. which articulates through cartilage to the second The second element is completely overlain by the pharyngobranchial; the other is capped by cartilage basibranchial plate. The second hypobranchials and connects to the posterolateral aspect of the

i_1 nLe_rt i

1 1 m m A 1

FIGURE 9. A. Lateral view of left hyoid arch, showing foramen in ceratohyal of 24 mm. Notol- ychnus valdiviae. B. Lateral view of left side of median structure of branchial arches, Mycto- phum brachygnathum, 79 mm. C. Dorsal view of median and left ventral halves of branchial arches, M. brachygnathum, 79 mm. D. Anteroventral view of left dorsal halves of branchial arches, M. brachygnathum, 79 mm. BB—basibranchials; BP—basibranchial plate; CB—cerato- branchials; CH—ceratohyal; EB—epibranchials; EH—epihyal; HB—hypobranchials; HH—hypo- hyal; IH—interhyal; PB—pharyngobranchials; PTP—pharyngobranchial tooth plates; TP—tooth plates. 26 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No.13 third pharyngobranchial. Further posterior, a small side of the triangle developed into a dorsal keel. projection, which has elongated into a slender head The keel is heaviest in Centrobranchus. The ven- in some forms, appears to be associated with one tral area of the pharyngobranchial is covered by a of the heads at the anterodorsal end of the third plate with moderate to strong teeth, which increase epibranchial. The gill filaments of the second arch in size posteriorly. In Myctophum asperum and end at this point. In Gonichthys and Centrobran- Gonichthys the tips of the individual teeth are chus the medial anterior head of the second epi- rounded to form many, closely-set pegs. In Centro- branchial has been lost. branchus the teeth of the third pharyngobranchial The second pharyngobranchial lies between the are highly modified as a series of small, rectangular first epibranchial and the third pharyngobranchial. plates set in even rows across the greatly enlarged Its anterior head is capped by cartilage and is pharyngobranchial. The plates are largest anteriorly closely associated with the anterior end of the third and decrease in size posteriorly. Very little space pharyngobranchial. A posterodorsal head articu- exists between the individual plates and rows, and lates by cartilage to the posterodorsal head of the the impression is of a highly efficient crushing first epibranchial. The anteroventral (oral) face is organ. Recently Hartmann and Weikert (1970) overlain by a plate covered with small teeth. In have found pelagic gastropods as food of Centro- Gonichthys and particularly Centrobranchus this branchus nigroocellatus. In most species of myc- bone is greatly reduced and the tooth plate is lost. tophids, the area of the third pharyngeal tooth plate In Centrobranchus all that remains is a small, slen- is considerably larger than that of the fourth. How- der bone considerably removed from the anterior ever, in Protomyctophum, Hierops, all Electrona end of the second epibranchial. but E. rissoi, most Diaphus and Notolychnus, the The third branchial arch consists of the five basic fourth tooth plate is equal in size or larger than bones, the median basi- and paired hypo-, cerato-, the third. epi-, and pharyngobranchials. However, the hypo- The basibranchial plate overlies the posterior branchials are lateral and ventral to the basibran- portion of the first basibranchial, the second and chial; this placement may explain why Supino third basibranchials, as well as the posterior portion (1901) did not report them. The anterior ends of of the third hypobranchials. The plate is narrow the hypobranchials bend ventrally and articulate anteriorly and broadens posteriorly over the third with the dorsal side of the urohyal wing. Gill teeth hypobranchials into a triangular area. It is always are present only on the most posterior lateral face one piece, and no suture lines are evident at the of the third hypobranchials. The posterior margin cartilaginous points of basibranchial articulation. of the third basibranchial is anterior to the posterior In most species the posterior end of the plate is margins of the third hypobranchials, and lies be- anterior to or at the posterior margin of the third tween them. The third ceratobranchial, although hypobranchials (A). In species with an enlarged shorter, is essentially the same as the ceratobran- plate, it extends behind the third hypobranchials chials of the first two arches. The epibranchial (P) (Table 5). The posterodorsal surface of the articulates through cartilage with the ceratobran- plate is covered with fine teeth. The anterior extent chial and the posterolateral face of the third of dentition is variable; in some species the teeth pharyngobranchial. A posterior head projects dor- do not extend forward of the second hypobranchial sally from the epibranchial and is often connected or the anterior area has a few, small, scattered tooth by a ligament to the lateral face of the fourth epi- patches ( — ). In other forms the teeth extend for- branchial; it supports the terminal portion of the ward of the second hypobranchials ( +) (Table 5) , gill filaments of the third arch. in some cases to the articulation point of the first The third pharyngobranchial is both variable hypobranchials. and complex in myctophids. Its posterior end artic- The fourth branchial arch consists of the three ulates through cartilage with the anterior ends of most posterior bones; the basi- and hypohyals are both the fourth epi- and pharyngobranchials. Pos- either indistinguishably fused to the anterior tip of terolaterally it articulates with the third epibran- the fourth ceratobranchial or, more likely, are chial. Its anterior end is closely associated with the represented by a small cartilage. The area between second pharyngobranchial and is often covered by the posterior ends of the basibranchial plate and the dentigerous plate of that bone. The shape of the third hypobranchials and the anterior ends of the third pharyngobranchial is usually triangular; the third and fourth ceratobranchials is entirely car- base of the triangle is the posterior articulation with tilaginous. The anterior ends of the fourth cerato- elements of the fourth arch. From the dorsal aspect, branchials articulate with each other and with the the area of the triangle is concave, with the median cartilaginous area, while the posterior ends articu- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 27

TABLE 5 CHARACTERS OF THE OPERCULAR BONES AND BRANCHIAL ARCHES (See text for explanation of characters)

4.1 Teeth Flag Margin Basibranchial Pharyngeal One Teeth Opercular Post. Basibranchial GENERA Preopercular Protomyctophum S A P 0-1 Hierops S A P 0-1 Electrona S A, P P 1-2 Metelectrona S A P 1 Hygophum S, D A, P P 1 Benthosema S A P 1-2 Diogenichthys S A P 0-1 Myctophum + S, D A, P P, A 1-2 Ctenoscopelus D A A 1 Symbolophorus + S, D A P, A 1-2 Loweina S P P 0 Tarletonbeania S P P 1 Gonichthys S P P 0 Centrobranchus S P P, A 0 Lobianchia S A A 1-4 Diaphus F S A, P P, A 1-2 Notolychnus S A A 0 Taaningichthys F S A P, A 1 Lampadena S P A 1 Lampanyctodes S A A 1-2 Stenobrachius S A A 1 Triphoturus S A, P A 1 Parvilux S A A 1-2 Lampanyctus F S A P, A 1-2 Lepidophanes F S A P, A 1-3 Ceratoscopelus F S A A 1 Gym noscopelus S A A 2-5 Nasolychnus S A A 3-5 Lam pichthys S A A 6 Notoscopelus S A A 2-3 Hintonia S P A 1-2 Scopelopsis S A A 1-2

late through cartilage with the anterior ends of the fourth epibranchial supports the end of the gill fourth epibranchials. The lateral, dorsal, and filaments of the fourth arch. The area posterior to medial faces of both cerato- and epibranchials bear this head and dorsal to the main body of the epi- gill teeth or tooth patches. The anterior end of the branchial is usually ossified. The greatest develop- fourth epibranchial articulates through cartilage ment again occurs in Centrobranchus where a large, with both the posterior end of the third pharyngo- dorsal keel is present on the posterior two-thirds branchial and the anterolateral face of the fourth of the fourth epibranchial. The fourth pharyngo- pharyngobranchial. A posterodorsal head of the branchial is extremely small and often represented 28 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13 by cartilage only. It is completely overlain by a dentigerous plate with strong teeth, and articulates with the third epi- and pharyngobranchials. It bears the largest and most posterior teeth in the oral cavity. In those species with pegs or plates on the third pharyngeal, all but Myctophum asperum re- tain normal teeth on the fourth pharyngeal plate. In M. asperum the anteriormost teeth are modified as pegs. Supino (1901) did not report the third and fourth pharyngobranchials in Hygophum benoiti, but I find these elements present in all myctophids examined, although the small fourth may be unossified. The fifth branchial arch is represented by the slender ceratobranchial, which has a tooth patch on the dorsolateral aspect. The anterior end articulates through cartilage with the corresponding member from the other side. The main shaft and posterior end of the fifth ceratobranchial are bound in the dense connective tissue of the floor of the pharynx. FIGURE 10. Lateral view of left pectoral girdle. A. Hygophum atratum, 61 mm. B. Stenobrachius nanno- Pectoral Girdle chir, 107 mm. CL—cleithrum; CO—coracoid; EX- The dermal elements of the pectoral girdle in- extrascapular; PR—proximal radials; PT—posttemporal; clude the posttemporal, supracleithrum, cleithrum, SCA—scapula; SCL—supracleithrum. The postcleithra are not figured. and two postcleithra. The scapula and coracoid are endochondral bones. No mesocoracoid was found in the myctophids examined (Fig. 10). often slightly overlaps the ventral expansion of the The terminology of Jollie (1954) is used for the posttemporal and lies anterior to it. The condition main bones of the pectoral girdle. However, the of one bone is apparently the result of an increase extrascapulars (tabulars of Jollie), bones associated in size of the dorsal element and a fusion of the two with, but not a part of, the pectoral girdle are prob- bones. However, in Loweina the dorsal element has ably not homologous to the tabulars, but to the been lost. One or both of the elements may be very lateral extrascapulars of crossopterygians, as Jollie poorly ossified and difficult to discern, even in (1954:77) himself states. cleared and stained specimens. Often the anterior The posttemporal is a forked bone that sus- and posterior edges of the dorsal element are pends the pectoral girdle from the cranium. The turned up, to form a shallow trough. The ventral dorsal fork articulates with the epiotic near the dor- element often bears small keels on the anterior and sal midline and closely approaches the tip of the posterior margins. The extrascapulars and the ven- dorsal fork from the other side. The ventral fork is tral expansion of the posttemporal underlie a por- shorter and attaches by a ligament to the opisthotic. tion of the sensory canal system. Three branches The ventral area of the posttemporal, where the apparently meet at the ventral expansion of the two forks join, is broadly expanded lateral to the posttemporal: the temporal canal which courses forks. The expansion extends ventrally over the anteriorly to the orbital region and passes over dorsal tip of the supracleithrum and dorsally along the ventral extrascapular; the posttemporal canal the upper fork of the posttemporal. The ventral which runs dorsally over the dorsal extrascapular margin may be folded over to form a closed tube to the midline; and the main branch of the lateral (C), an open tube (0), or it may be flat ( — ) line canal, which runs ventrally through the post- (Table 6). The anterior portion of the lateral line temporal tube, if present, and over the dorsal por- canal passes through the tube when present. tion of the supracleithrum for a short distance In lanternfishes, one or two (Table 6) extra- before turning posterior as the lateral line (Jollie, scapulars are found slightly anterior and lateral to 1954:26, Fig. 9A). the posttemporal. When two are present, the dorsal The supracleithrum is a straight, elongate bone bone is the smaller and overlies the dorsal fork of which dorsally underlies the ventral tip of the post- the posttemporal. The larger ventral extrascapular temporal and ventrally overlies the dorsal part of 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 29

TABLE 6 CHARACTERS OF THE PECTORAL GIRDLE (See text for explanation of characters) Tube Tube

Shelf CHARACTERS Posttemporal Supracleithral Extrascapulars Cleithral Proximal Radials GENERA Pectoral Fin Rays Protomyctoph urn 4 0-2 14-17 Hierops 4 0-2 15-18 Electrona —, 0, C —, 0, C 4 0-7 12-16 Metelectrona 4 1 14 Hygophum o, c 4 9-11 12-16 Benthosema —, 0 4 2-10 12-14 Diogenichthys 4 8-12 10-13 Myctoph urn o 0, C 4 0-6 13-22 Ctenoscopelus 4 0 17 Symbolophorus o 0, C 4 0-2 13-19 Loweina 3 7 10 Tarletonbeania 0, C 3 0 13-15 Gonichthys 4 0 12-13 Cent robranchus 4 2-3 14-17 Lobianchia 0, C 0, C 3 5 11-12 Diaphus 0,C 0,C 3,4 1-7 10-14 Notolychnus 4 0 14 Taaningichthys o 4 13-17 Lam padena 4 16-17 Lampanyctodes 0 4 13-14 Stenobrachius 4 10-11 Triphoturus o 4 9-? Parvilux 4 13 Lampanyctus o, C o, c 3,4 0-14 Lepidophanes 0, C 4 10 13-14 Ceratoscopelus 4 12-14 Gymnoscopelus 0, C 0, C 4 13-16 Nasolychnus 0, C 0, C 3, 4 12-15 Lampichthys 0 4 14 Notoscopelus 4 11-12 Hintonia 4 14-15 Scopelopsis 4 11-12

the cleithrum. A number of shelves project from area of the supracleithrum to the first vertebrae. the main shaft of the supracleithrum for all or part The cleithrum, the largest bone in the pectoral of its length. An anterior shelf and a lateral shelf girdle, is complex in shape. The main shaft forms are most prominent. In some forms, the postero- a wide curve with the concavity directed anteriorly. dorsal margin forms a trough for a short length of The dorsal portion of the shaft underlies the supra- the lateral line canal. The trough may be absent cleithrum, while the ventral portion curves ante- ( — ), open (0), or closed (C) (Table 6), that is, riorly and slightly medially to meet its fellow from roofed over with weak ossification for part of its the other side in the midline under the pharynx. length. A strong ligament runs from the ventral They are tightly bound together by connective 30 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 tissue. A number of wings, crests, or shelves project postcleithrum superior and the coracoid. from the main shaft of the cleithrum. Most promi- There are usually four proximal radials which nent is the lamina posterior, a thin ossification display various changes in shape and degrees of which extends posteriorly from the medial portion fusion. Numbering from dorsal to ventral, the first of the shaft above the scapula. This extension over- three radials articulate on the posterior margin of lies the dorsal edge of the scapula. A lateral shelf the scapula and the fourth articulates on the cora- projects posterolaterally from the ventral half of coid or at the scapula-coracoid juncture. Each the cleithrum. A pronounced posterior shelf from radial is typically hour-glass in shape although the ventral half of the main shaft may be present weaker secondary ossification may fill in some or ( + ) or absent ( — ) (Table 6). The anteroventral all of the middle region. Extensive ossification on process of the coracoid articulates on the lateral the ventral margin in some species expands the face of the posterior shelf if present; if the pos- fourth radial to large size. The radials usually in- terior shelf is absent, the coracoid process articu- crease in length and slightly decrease in width from lates on the medial face of the lateral shelf. dorsal to ventral. Both ends of the radials are often The rectangular or trapezoidal scapula is the fused to each other. When all of the middle space main support for the radials and fin rays of the is ossified, the radials are considered fused and con- pectoral fin. The anterior margin articulates with sequently reduced in number to three (Table 6). the main shaft of the cleithrum medial to the lateral Radials one and two, two and three, or three shelf, the ventral edge joins the dorsal margin of and four may become fused to reduce the radial the coracoid through cartilage, and the dorsal mar- number. gin is slightly overlapped by the lamina posterior. A row of distal radials, one per ray, is found The dorsal half of the posterior margin is free and between the bases of the pectoral fin rays. They the ventral half articulates with the proximal are usually cartilaginous, but are stained in some radials, usually the three most dorsal ones. Dorsal specimens. These radials appear to be calcified car- to the first radial, a small projection on the scapula tilage rather than bone. The number of calcified marks the articulation point of the first and occa- radials varies from none to 12 (Table 6). The cal- sionally the second pectoral fin ray. The middle of cification is strongest in the most dorsal distal the scapula is pierced by a scapular foramen which radial, which lies between the bases of the second varies in size and somewhat in position. pectoral ray; the ossification decreases ventrally. The coracoid is ventral to the scapula and pos- The last calcified radial is usually very small and terior to the cleithrum. Its dorsal margin is slightly the calcification may be only on one side of the separated from the scapula by a thin strip of midline, suggesting a paired origin for the radials. cartilage. Posteriorly, the fourth radial either artic- Only in Diogenichthys are the distal radials for all ulates with the coracoid or straddles the scapula- rays but the first calcified; the first pectoral ray coracoid juncture. The dorsal portion of the never has a calcified distal radial. coracoid articulates anteriorly with the main shaft The first and occasionally the second pectoral fin of the cleithrum dorsal to the end of the posterior ray articulate on the scapular peg dorsal to the first shelf if one is present. The main body of the cora- proximal radial. All other rays articulate with the coid bends anteroventrally and narrows to a rod proximal radials. The base of the first ray is greatly which articulates with the ventral portion of the enlarged on the medial half of the lepidotrich. It cleithrum on one of two shelves. A gap is present may be that the first distal radial has fused to the between the dorsal and anteroventral articulations, base of the medial half of the first ray, as no free the coracocleithral fenestra. Only in Tarleton- distal radial was found dorsal to the second ray. beania is the fenestra completely ossified, so that The rays decrease in length and diameter ventrally; the coracoid articulates along its entire anterior the last two or three rays may be extremely short margin with the cleithrum. and thin. In some genera, and particularly in some The postcleithrum superior is a slightly elon- species of Lampanyctus, the pectoral rays, radials, gated, laminar bone which lies medial to the lamina and even the scapula and coracoid are poorly posterior of the cleithrum, the scapula, and the dor- ossified. In L. achirus no ossification is present, sal portion of the coracoid. Its ventral margin is although the outlines of four proximal radials are lateral to the posterodorsal portion of the post- visible. What appear to be minute remnants of cleithrum inferior. pectoral ray-bases are weakly attached to the The postcleithrum inferior has the shape of an radials. With the exception of this species, the elongate triangle, with a thin rod extending pos- number of pectoral rays varies from nine to 22 teroventrally. The dorsal portion underlies the (Table 6). 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 31

Pelvic Girdle TABLE 7 CHARACTERS OF THE PELVIC GIRDLE The pelvic girdle consists of a pair of bones that (See text for explanation of characters) form a triangle in the ventral body wall between the verticals of the origins of the pectoral and dor- sal fins (Fig. 11). The main portion of the pelvic bone is rodlike and meets its fellow from the oppo- t site side in the midline at the anteriormost point of Ossif. amen the girdle where the tips are joined by connective igL tissue. The area medial to the main shaft of the l hia pelvic bone is usually slightly ossified ( — ), as a c Principal Rays pubic plate. However, in some species the ossifica- GENERA Pubic Plate Is tion is so extensive that the pubic plates meet in the midline posterior to the anterior tips of the Protomyctophum 8-9 main shaft ( + +). The bones are not fused in this Hierops 8 S, F region, but the median ossifications slightly over- Elect rona + 8 S, F lap in the midline. In other species the anterior Metelectrona 8 median ossification is moderate and does not meet Hygophum 8-9 in the midline ( + ) (Table 7). Posteriorly, the Benthosema 8 S, F pelvic bone is broad and serves as the attachment Diogenichthys 8 point for the pelvic rays. The posterior margin is Myctophum + 8 S. F irregularly sculptured in the articulation area. The Ctenoscopelus 8 posterior region extends medially as an ischial ossi- Symbolophorus + 8 S, F fication composed of two parts which may or may Loweina 8-9 not be completely fused. The main portion ends in Tarletonbeania 8 cartilage which meets its fellow in the midline; the Gonichthys 7 two are joined by strong connective tissue. The Cent robranchus 8 posteriormost portion ends before the midline in a Lobianchia ++ 8 short ligament which runs to the medial spinalis Diaphus ++ S, M 8 S, F ventralis tendon, a long pair of tendons that extend Notolychnus 6 '7 from the tips of the cleithra to behind the pelvic Taaningichthys S. M 8 S, F bones (Jollie, 1954: Fig. 35). The ischial ligament Lam padena 8 does not join the ligament from the other side in Lampanyctodes ++ 8 Stenobrachius M, L 8 Triphoturus 8 Parvilux 8 Lampanyctus 8 S, F Lepidophanes M, L 8 Ceratoscopelus 8 S, F Gymnoscopelus 8-9 S, F Nasolychnus 8 S, F Lam pichthys 8 Notoscopelus + 8 Hintonia 8 Scopelopsis 7-8

the midline, but two general conditions are present. Usually the ligament is very short and runs directly to the tendon of that side (S). In some forms the ligament is longer and runs posterior before joining the tendon (L). A few forms display FIGURE 11. Ventral view of pelvic bones of Lobianchia gemellari, 57 mm. Anterior to left. IO—ischial ossifica- intermediate states between the two extremes (M) tion; PP—pubic plate. (Table 7). 32 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13

There are eight main pelvic rays in each fin of for a single species is two, some species may vary almost all myctophids, plus a rudimentary spine by as many as four vertebrae. The same is true for (Patterson, 1964:444) or splint (Gosline, 1961:18, dorsal and anal counts of which the range found Fig. 5B) present at the base of the outermost ray. for the family is 10 to 26 and 12 to 27 respectively. The splint is a single, asymmetrical, unsegmented Rosen and Patterson (1969:451) reported element and not a typical paired and segmented ". . . the occurrence of a single dorsal and anal soft ray. Patterson (1964:445) considered the spine in at least one species of the myctophid genus splint a remnant of a holostean fulcral scale. The Lampanyctus . . ." Four species of Lampanyctus splint was present in all forms except the poorly are listed in the section on materials examined; of ossified Notolychnus valdiviae. In only two species, these L. lacerta is a junior synonym of Diaphus Gonichthys tenuiculum and Notolychnus valdiviae, dumerili. None of the myctophids examined in the does the pelvic count constantly vary from eight present study, including the four species listed by (Table 7). In all other variations, nine rays in five Rosen and Patterson, had any indication of dorsal species and seven rays in one, the difference was or anal spines, which are commonly defined as limited to only one specimen of the species series, single, unpaired elements without segmentation or and often to only one side. With the two specific branching. The first one or two elements of either exceptions, the pelvic ray count for the family can fin are often so short that segmentation is not pres- be considered relatively constant at eight; variation ent. However, even the smallest elements are com- occurred in less than two per cent of the specimens posed of bilateral halves with no fusion occurring examined. The innermost pelvic ray is broadly ex- in the midline; overlapping of the halves in the panded at its base, and the next two or three rays midline is apparent in larger elements, but with- articulate on this base (Jollie, 1954:Fig. 21B; out fusion. Gosline et al., 1966:Fig. 3E and 3F). The ex- panded base was considered a fused pelvic radial Caudal Skeleton by Gosline (1961:20) and Gosline et al. (1966:4); Two sets of nomenclature have recently been the enlarged base of the first pectoral ray in myc- proposed (Gosline, 1960; Nybelin, 1963) for the tophids may also represent a fused radial. Between complex elements of the teleost caudal skeleton the bases of the pelvic rays lateral to the expanded (Fig. 12). Gosline considered the first ventral inner ray are two ossified pelvic radials which hypural as that element which usually bears a lat- appear to be calcified cartilage rather than true eral flange near its base and behind which emerge bone. Pelvic radials in a number of primitive tele- osts were described by Gosline (1961:19-21). In most Myctophidae the radial calcifications are paired, on the dorsal and ventral side of the space between the lepidotrich halves, resulting in four separate calcifications (S). The two radials appear to be single elements, however, with cartilage fill- ing the uncalcified space. In some forms the radials are solidly fused into two single elements (F) (Table 7).

Axial Skeleton Although description of the detailed morphol- ogy of the vertebrae, ribs, median fin supports, and rays is left for future studies, meristic counts were made on all cleared and stained specimens. Although vertebral counts of many of the rarer genera are given for the first time, the range of variation presented (Table 8) does not include all extremes encountered when a large series is ex- amined (cf. Moser and Ahlstrom, 1970: Tables 1, 2, and 3), due to the relatively small numbers of specimens prepared for each species. Total num- FIGURE 12. Lateral view of left side of caudal skeleton of Protomyctophum normani, 54 mm. EP—epural; ber of vertebrae for the family range from 28 to HS—haemal spine; HY—hypural; NS—neural spine; 45; although the typical range in vertebral number TV—terminal vertebra; UN—uroneural. 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 33

TABLE 8 CHARACTERS OF THE AXIAL SKELETON (See text for explanation of characters)

CHARACTERS Abdominal + GENERA Dorsal Rays Anal Rays Vertebrae Caudal Vertebrae Protomyctophum 12-14 15-27 36-41 14-18+20-25 Hierops 11-13 20-27 36-42 15-16+21-26 Elect rona 13-15 18-22 33-40 14-17 + 18-25 Metelectrona 14 21 37 15+22 Hygophum 13-14 18-23 34-37 15-16+18-22 Benthosema 12-14 17-21 32-36 14-15+18-21 Diogenichthys 10-12 15-17 30-33 13-14+17-19 Myctophum 11-15 17-25 35-44 15-19+20-27 Ctenoscopelus 13 22 38 15+23 Symbolophorus 13-16 20-21 37-40 15-16+21-25 Lowe m a 12-13 16 39 18+21 Tarletonbeania 11-14 17-18 40-41 17-18+23-24 Gonichthys 10-11 18-19 38-39 14-15+23-25 Cent robranchus 10-11 17-18 36-38 15-16+21-23 Lobianchia 15-17 14 34-35 15-16+19 Diaphus 12-18 12-17 32-37 14-16+16-21 Notolychnus 11 13 28-30 12-13+16-17 Taaningichthys 12-13 13 35-41 16-20 + 18-21 Lam padena 15 13-14 36-37 15-16+20-21 Lampanyctodes 13-14 16-17 37-38 16+21-22 Stenobrachius 12-15 14-16 36-38 15-16+21-23 Triphoturus 13-15 15-18 32-35 15-16+17-19 Parvilux 15-16 16-18 37-38 15-16+21-22 Lampanyctus 12-16 16-21 31-40 13-17+18-24 Lepidophanes 12-15 13-15 32-35 15-16 + 17-21 Ceratoscopelus 13-14 13-14 36-38 15-17+19-21 Gymnoscopelus 16-21 17-22 42-44 15-19+25-27 Nasolychnus 16-19 18-20 41-45 16-18+24-27 Lampichthys 16-17 22 41 16+25 Notoscopelus 22-26 19-20 37 16+21 Hintonia 15 13-14 38-39 16-17+21-23 Scopelopsis 22 23-24 38-39 16+22-23

the blood vessels of the haemal canal. The vertebra the postterminal centra of Gosline the ural verte- on which the first hypural articulates was termed brae, and the preceding vertebrae were termed the terminal vertebra, those preceding—the preter- preural vertebrae. If the nomenclature were re- minal vertebrae, and any centra following—the stricted to Elops, or other primitive teleosts alone, postterminal centra. Nybelin, using the caudal Nybelin's scheme might be preferred. The self- skeleton of Elops as an example, presented a series contradictory term postterminal centra would be of logical arguments for considering the first ven- eliminated and the functional aspect of the last tral hypural of Gosline as the last haemal spine, haemal arch element would be emphasized. How- and the next ventral element as the first hypural. ever, in osmerids and stomiatoids (Weitzman, The bone in question serves two functions; proxi- 1967a, 1967b), neoscopelids, and myctophids, and mally it is the last element of the haemal arch and many other higher teleost groups (Gosline, 1961), canal, while distally it is expanded and supports distinctive changes have taken place in the caudal some of the principal caudal rays. Nybelin called skeleton which make the terminology of Nybelin 34 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13 impractical and confusing. In the above-mentioned groups, the terminal vertebra and the first post- terminal centrum of Elops have apparently fused, so the ventral hypurals articulate with a single ele- ment. Also, in some myctophids at least, the three ventral hypurals fuse into a single element, and the lateral flange expands to cover most of the base of this fused structure (see Fig. 14). If the nomencla- ture of Nybelin were followed, the vertebral ele- ment would be composed of the preural and the first ural vertebrae, and the fused hypural struc- ture, functionally and morphologically one ele- ment, would be composed of the last haemal spine and the first two hypurals. I think it less ambiguous to follow the terminology of Gosline (1960), while realizing that the first hypural is also the last func- tional element of the haemal canal. The latter portion of Nybelin's (1963) paper was concerned with the derivation of the uroneu- FIGURE 14. Lateral view of left side of ventral part of rals. He proposed that the uroneurals are derived caudal skeleton of Centrobranchus andreae, 51 mm, from the dermal scale rows of the caudal fin, as showing fusion of ventral three hypurals and complex hypural flange. found in Acipenser and Polyodon, rather than from neural arches of aborted centra as suggested by Regan (1910). Nybelin marshalled evidence he proposed that the elements previously termed from both living and fossil primitive teleosts, but uroneurals be called urodermals, to emphasize their admitted that the limited embryological evidence derivation from dermal scales. However, the con- is contradictory. In accordance with his hypothesis, tradictory embryological evidence concerning the derivation of the first uroneural is reinforced by the development of this first element in mycto- UN2 phids. Nybelin cited embryological studies of sal- monids that suggested the first uroneural is of complex origin, part preformed in cartilage, as a neural arch would be, and part without a cartilage precursor, as a dermal element would be. The first uroneural in post-larval myctophids (Fig. 13) develops much as a neural arch would, and the same element in adults (Fig. 12) appears to be a modified neural arch. Until the question is answered by detailed embryological studies, as Nybelin suggested, the older term, uroneural, will be retained in this study. Derivation of the sec- ond uroneural in myctophids is unclear, and the two uroneurals in myctophids may have different origins. The expanded bases of the neural and haemal arches of the preterminal vertebrae were termed median neural and haemal plates by Gosline (1960) and pre-epurals and prehypurals by Jollie (1954). Since the epurals and hypurals appear similar in position and form to the neural and haemal spines, and may be homologous to these structures, and not the arches, the terminology of Gosline is followed. FIGURE 13. Lateral view of left side of part of caudal skeleton of Gymnoscopelus aphya, 28 mm. Abbrevia- The preterminal vertebrae have expanded neural tions as in Fig. 12. and haemal arches and median neural and haemal 1972 stays. Theplatesarereducedinanteriorvertebrae. structures arereinforcedbyanumberofossified last neuralandparticularly haemalspinesare plates, whichcontributetothearchesandfrom The firstpreterminalvertebra lacksaneuralspine, which mayberepresentedby thefirstepural.The posterior limitofeachvertebra.Vertebralandarch which theneuralandhaemalspinesemergeat Scopelopsis Hintonia Notoscopelus Lampichthys Nasolychnus Cent robranchus Gymnoscopelus Lepidophanes Lobianchia Diaphus Bent hosema Metelectrona Protomyctophum Lam panyctus Parvilux Lampadena Stenobrachius Symbolophorus Gonichthys Ceratoscopelus Notolychnus Lowe Myctophum Diogenichthys Hygophum Elect rona Hierops Lam panyctodes Ctenoscopelus Taaningichthys Tarletonbeania Triphoturus GENERA

V

m a

OSTEOLOGY ANDRELATIONSHIPSOFLANTERNFISHES 2 2-3 2-3 2-3 2 3 2 2-3 1-3 3 3 2-3 2-3 3 3 3 3 2-3 2-3 2-3 2-3 2-3 3 3 3 3 3 3 3 3 3-4 3 A, A, A, A, A, A A A P A P P A A A A A A A A A A A A A A A A A A A A Origin P P Epural P P P CHARACTERS OFTHE (See textforexplanationofcharacters) 3-4 2 2-4 4 4 3-4 3 3 4 4 4 4 4 4 4 1 1 4 4 4 4 4 4 4 4 4 4 3-4 3-4 3-4 3 4

DorsalHypurals 2-3 2 1 1 3 3 3 3 2-3 2-3 2-3 2-3 2 1 3 3 3 3 3 3 3 2 2-3 2-3 3 3 3 3 3 2-3 3 3 TABLE Ventral Hypurals CAUDAL fused inadultsandoverlain bythecomplexuro- first principalcaudalrayinthedorsalandven- Ahlstrom, 1970).Thesecentra arecompletely larval specimens(Fig.13; tral series. bral centrawhichareapparentinanumberofpost- flattened; theselastspinesoftenarticulatewiththe 9 The terminalvertebraisformedfromtwoverte- —, +,++ +, ++ —, + —, + —, + SKELETON ++ ++ ++ ++ ------+ + + + _ — — + + _ — _ _

HypuralFlange +, ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ------+ + + + + — — —

Procurr.Rays Fused Jollie

10 10 10 10-11 10-13 10-12 7-10 7-9 7 5-8 7-9 7-11 7-9 7-8 7-8 8 8 6 6-8 8-9 8-9 8-10 8-13 8-10 8-10 6-7 6-7 5-7 5-6 8 6-8 5-7 t 1954;Moserand DorsalProcurr. Rays 11 13 11-15 12 10-15 11-15 9 7-9 7-9 9 9-10 6 7-9 7-9 7-9 7 5-7 5-6 6-9 6-8 6-8 6-7 7-8 8-9 8-9 8-9 6-9 6-7 6-7 6-10 5-6 8-9 Ventral Procurr.Rays 35 36 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13 neural structure. In all three neoscopelid genera, principal rays are unbranched. From one to four the postterminal centrum is always visible in large procurrent rays are segmented; the others are un- (100 mm) specimens. The first uroneural in myc- segmented, but all are paired. The degree of flexi- tophids fuses to the terminal vertebra and obscures bility of these rays, considered phylogenetically the limits of the urostyle. The second uroneural is important by Fraser-Brunner (1949), appears to paired and overlies the dorsal margin of the fourth be the result of the amount of distal fusion between dorsal hypural. the two elements of each pair [ none or slight ( — ), The epurals of adult specimens are always sur- moderate ( + ), or great ( + +) (Table 9)], the rounded by secondary ossification. Their fusion, diameter of each element, and the amount of mus- length, and width vary within the family. Epurals culature around the bases of the rays. The halves two and three may be partially or completely of the first, most anterior, ray of each series may be fused, resulting in only two epurals (Table 9). If slightly fused, even in forms with flexible rays. partially fused, the structure has a bifid base. Three Although the elements may be fused for most of separate and distinct epurals is the usual condition their length, they are clearly derived from paired in myctophids, but in one specimen of Tarleton- halves in all specimens examined; the decision to beania one epural was found and in another speci- call the elements procurrent caudal spines (Rosen men of Electrona four epurals were present. The and Patterson, 1969:454) must be based on a dif- length of the first epural is variable; it originates ferent terminology. The halves of the segmented over the anterior portion of the terminal vertebra procurrent rays are never fused. in most genera (A) or over or behind the posterior In two genera, distinct morphological differ- margin of the terminal vertebra (P) (Table 9) in ences are apparent in the first few procurrent rays a few species. (Fig. 15). In Lepidophanes longipes the procur- The hypurals show various degrees of fusion rent rays are slender, as is typical for the family with the posteroventral edge of the terminal verte- (Fig. 15A). In L. guentheri the rays are broadened bra and urostyle and with each other. Young speci- and in the ventral series a hook or spine forms on mens clearly show the four dorsal and three ventral the posterior edge of each ray where it emerges hypurals (Fig. 13). In counting hypurals, if the from the body (Fig. 15B). The hooks are further suture line is evident for more than half the length developed in Ceratoscopelus townsendi (Fig. 15C), of the hypurals, they are considered separate. and show extreme development in C. maderensis The number of hypurals varies from two to seven (Fig. 15D); in both species hooks are apparent in (Table 8); the extreme condition of two hypurals both dorsal and ventral series. The number of pro- results in solid dorsal and ventral plates. The sec- current rays in dorsal and ventral series varies both ondary ossification between the dorsal and ventral series of hypurals varies from a large amount (Fig. 12) to almost none (Fig. 14), with con- siderable intraspecific variation. The proximal one- third to one-half of the anterior edge of the first ventral hypural is raised and forms a lateral flange (Gosline, 1960). The flange may be moderate ( — ), well developed ( + ), or developed into a complex structure overlying most of the proximal portion of the ventral hypurals ( + +) (Table 9; Fig. 14). The principal caudal ray count for the family is ten dorsal and nine ventral rays. One specimen each of three different species, less than one per cent of the specimens examined, had counts of ten plus ten, nine plus nine, or nine plus eight. The principal rays are easily distinguished by counting out from the midline; the last ray of each series is the largest in both diameter and length. The last principal ray of each series is usually simple or branched only at the distal tip. All other principal FIGURE 15. Lateral view of left side of anteriormost procurrent caudal rays. A. Bolinichthys longipes, 45 rays are branched. mm. B. Lepidophanes guentheri, 57 mm. C. Cerato- All of the procurrent caudal rays anterior to the scopelus townsendi, 65 mm. D. C. maderensis, 62 mm. 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 37 intra- and interspecifically (Table 9). In most spe- The infracaudal organ may consist of small, dis- cies, the dorsal series contains one more ray than crete, poorly developed, luminous spots, with or the ventral series, while in some species the ventral without margins of dark pigment, numbering from series contains one to three more rays. one to five (S). In a few forms the individual lumi- nous spots are large and overlap slightly to form a LUMINESCENT ORGANS gland with distinct divisions (D). The infracaudal gland may be a large, undivided structure bordered Luminous Tissue by black pigment (L). The final form of the gland In addition to the series of photophores present may be a long, thin structure composed of poorly in myctophids, other luminous tissues occur on defined and overlapping luminous plates. No pig- many forms. The presence of luminous glands or ment separates the plates and the divisions are diffi- organs on the caudal peduncle is the most common cult to discern (T) (Table 10). condition. The caudal luminous glands of lantern- The supracaudal glands show more variation in fishes are variable in their structure and form, but form than the infracaudal organs. They may con- the full scope of variation has never been described sist of from four to seven small, rounded, luminous nor utilized as a taxonomic character. The follow- spots, completely separate and surrounded by black ing descriptions are based only on low-power pigment (S) ; a single, small spot without pigment microscopic examination; an histological survey of (0) ; a long, undivided organ outlined by black pig- the different types of glands is needed. The caudal ment (L); a large gland formed by the coalescence luminous structures usually become apparent well of discrete spots, with the divisions marked by after metamorphosis from the larval stage, after black pigment (D) ; a long, thin structure of over- the photophores are distinct; a correlation with the lapping luminous plates, without pigment marking attainment of sexual maturity is probable. Sexual off the divisions (T) ; or a single strand of undi- dimorphism in the presence or absence and/or vided luminous tissue without any pigment border form of the caudal glands is common (Table 19). (U) (Table 10). Considerable variation is appar- The commonest type of sexual dimorphism in- ent in some genera and even in some species. The volves the presence of only supracaudal glands in most striking development of caudal luminous males and only infracaudal glands in females. In organs has occurred in the genera Taaningichthys Tarletonbeania and Loweina, however, the females and Lam padena, where the luminous tissue is en- lack any caudal glands, while in Notolychnus the larged and translucent. size of the supracaudal gland differs in the sexes In some forms luminous tissue is present on and no infracaudal gland is present. Caudal glands areas other than the caudal peduncle (Table 10). are completely lacking in a few groups (Table 19) The tissue is usually in the form of small patches and both supra- and infracaudal glands are present that are often lost with the scales during capture. in each of the sexes in several genera. These luminous patches are not as differentiated as

FIGURE 16. Hypothetical myctophid, showing photophore terminology of all the various photo- phore groups found in lanternfishes. Individual photophores of a series are counted towards the tail. The following definitions differ from, or are in addition to, those of Fraser-Brunner (1949): CP—cheek photophore; LT—patches of luminous tissue; INGL—infracaudal luminous gland; SUGL—supracaudal luminous gland. After Nafpaktitis (1968). 38 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No.13 either the caudal glands or photophores; there is In a few forms, notably species of the genera no marginal pigment nor reflecting layer and the Diaphus and Gymnoscopelus, the orbital organs size and form of the tissue is variable. Luminous have become greatly enlarged and modified. Lumi- patches are often associated with the bases of the nous tissue in some species covers much of the dorsal, anal, pectoral, pelvic, and adipose fins; the anterior region of the snout. The enlargement of patches may be present on the sides of the body, orbital organs and the lack of caudal luminous particularly above the lateral line in front of the glands in these two genera is probably correlated. dorsal fin and on the head, between the orbits. In The antorbital organs usually have a distinct shape some forms each body scale appears to have a tiny for each species and are often sexually dimorphic. spot of luminous tissue. Apparent luminous tissue Fraser-Brunner (1949) suggested that the devel- is present on the posterior half of the iris in Taan- opment of luminous orbital organs inhibits the ingichthys and three species of Lepidophanes. Pre- growth of bone or vice versa. He remarked that sumed luminous tissue has been found on the dor- the luminous orbital organs develop only where sal part of the iris in one species of Lam padena there are gaps in the circumorbital series of bones. (Nafpaktitis and Paxton, 1968). I find very limited evidence to support this view. The orbital organs, found in front of and below The terminology of the bones of the snout used by the orbit, often have the appearance of body pho- Fraser-Brunner (1949:1029) can presumably be tophores, but because of the occasionally extensive identified as follows: supraorbital =supraorbital ex- development of these organs, are considered modi- tension of frontal; preorbital and posterior bone of fied luminous tissue (Fig. 16). The Dn is the nasal capsule = antorbital; suborbital =first circum- orbital organ located above the nasal apparatus; it orbital. The ethmoidal crest of Fraser-Brunner and is separate from the luminous tissue over the eye other authors is actually the midline crest of the in the genera Lepidophanes, Ceratoscopelus, and frontals; the ethmoidal crest is hidden below and Lam pichthys, contrary to the definition of Bussing between the medial edges of the nasals. The ant- (1965:208). The Vn has been defined as that orbital is associated with the posterior wall of the organ located below the nasal apparatus (Fraser- nasal capsule and is not functionally a part of Brunner, 1949, among others). To account for the circumorbital series. The greatest reduction organs situated directly behind the nasal appara- of the antorbital bone is found in the slendertailed tus, the definition of the Vn has recently been ex- genera Loweina, Tarletonbeania, Gonichthys, and panded to include all organs beneath the level of Centrobranchus, and is correlated with a modifica- the dorsal margin of the nasal apparatus (Nafpak- tion of the nasal bone, not with an increase in the titis, 1968). The suborbital organ (SO) is under size of the orbital organs. The horizontal ridge of the orbit and lies over either the first or second the suborbital (Fraser-Brunner, 1949:1065) is the circumorbital bone. In some species with an SO, ventrally turned dorsal border of the first circum- Electrona carlsbergi, Metelectrona sp., and Ben- orbital, and is found in most genera, regardless of thosema suborbitale, the organ apparently repre- the development of the Vn. In Electrona carlsbergi, sents a Vn that has moved posteriorly; no Vn in the SO lies in a cup-shaped depression in the sec- the forward position is present in these species. In ond circumorbital; however, no bone modification species of Diaphus with an SO, the organ is in addi- is present below the similarly situated SO in tion to the Vn. Metelectrona sp. or Benthosema suborbitale. The Typically both Dn and Vn are small and backed variations in other bones of the snout region of by black tissue. The Dn usually lies just under the lanternfishes apparently are not correlated with the anterolateral margin of the frontal, on top of the development of luminous tissue. dorsolateral corner of the lateral ethmoid. The Vn is typically found just posteroventral to the nasal Photo phores rosette, between the antorbital and lateral ethmoid, The terminology of photophores follows that of or on the anterodorsal corner of the first circum- previous authors, notably Brauer (1904), Bolin orbital. The latter is usually folded ventrally so the (1939), and Fraser-Brunner (1949) (see Fig. 16). luminous organ lies on the folded corner of bone, Fraser-Brunner discussed the evolution of differ- just outside the membrane that encircles the orbit. ent photophore patterns in relation to observed In some forms, one or both organs lack the margin changes in scale rows in lanternfishes. The varia- of black pigment and their presence is difficult to tions in stable photophore groups are summarized discern, especially in specimens with damaged (Table 11), so that the photophore patterns may be heads. The presence of a Dn and/or Vn is usually integrated with the osteological characters in the constant for a given genus (Table 10). taxonomic definitions given in the next chapter. The PHORES inclined sothatalinethrough thetwo The raised series followsFraser-Brunner definitions ofa having 1972 Scopelopsis LAM Ceratoscopelus Gymnoscopelus Hintonia Notoscopelus Nasolychnus Stenobrachius LAM Lampanyctus LAM Parvilux Triphoturus Lepidophanes CENT Gonichthys Diaphus Lobianchia Notolychnus Symbolophorus Ctenoscopelus Taaningichthys Tarletonbeania Loweina Hierops Benthosema Protomyctophum Electrona Myctophum Metelectrona Hygophum Diogenichthys The PVO GENERA pichthys panyctodes robranchus padena (4), PO runs forwardofthe one series iseitherhorizontalorvery slightly seriesiseitherlevel or the

PHOTOPHORE

PHOTOPHORE PO, OSTEOLOGY ANDRELATIONSHIPSOF and raised distinctlyoutof ------+ - - - - - + - PO,

PO, series beinglevelor (1949:1039). areraised

( —), ( CHARACTERS OFTHELUMINOUSORGANS (See textforexplanationofcharacters) H), PVO the

is sharply Caudal Glands (3, 5). PO photo- 4 is TABLE —, U D-T S, D - _ - — T T T — — T T S S T — L L S S S S S S S S S S S ?

InfracaudalGland site themiddleorupperend of the pectoralbase the ventral tothepectoralbase(V), orisdorsaltothe base the with theconnectinglinegoingthrough inclined sothattheconnectinglinerunsthrough 10 PO, PO, ( S, 0,U S, 0,D D). T, — 0, L D-T S, L S, 0 _ (V).The — orslightlybehindit(A),isvertical, _ — U T T D L L U T T T T 0 D L T S L S L L S

SupracaudalGland The PLOiseitherventralto (V),oppo- LANTERNFISHES (D). —, + ------+ ------PV0 _ _

Luminous Tissue The 2 iseitherinfrontofor VO series iseitherlevel A a (0),

or dorsalto or behind > a

39 40 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 or slightly arched ( — ) or the VO, and/or VO, is experience and biases of a given investigator. Since elevated (2, 3). The distinction between a raised a number of taxonomic decisions will be made in A0a and a Pol photophore is slight. A Pol is this paper, it is considered relevant to outline defined as any photophore between the A0a and briefly my ideas concerning supraspecific taxa. In A0p series which is above a horizontal line tan- an evolutionary study, the designation of a tribe, gent to the dorsal margin of the last, level A0a genus, or subgenus serves a number of purposes. photophore. The number of Pol photophores var- The first, and most important, is to designate ies from none to three (0-3). The number of Prc monophyletic lines of evolution. The designation photophores varies from one to nine (1-9). Noto- of higher taxa also indicates that all members of a lychnus is unique in having four photophores high given taxon are more closely related to each other above the lateral line near the dorsal profile. While than to any members of another, equivalent taxon. the presence of a Bu photophore on the cheek just Finally, it is practical to divide a large number of dorsal to the posterior end of the maxillary is vari- forms into units that are easier to discuss and men- able within genera, the presence of large photo- tally manipulate. While other purposes have been phores in the middle of the cheek is more constant; suggested for the establishment of a formal higher cheek photophores vary in number from none to classification (see Warburton, 1967), those dis- seven (0-7) (Table 11). cussed above are the only ones that will be taken Secondary photophores are extremely small into consideration in this study. organs, usually about one-third the size of the Although it is relatively simple to list the func- primary photophores. Secondary photophores may tions of a higher classification, it is much more be absent ( — ), restricted to the scales immediately difficult to select criteria for the establishment of above and below the lateral line (LL), or present any given taxon. More than sixty osteological char- under every scale on the body and even on the acters are listed in the preceding tables and text. head ( + ) (Table 11). In Scopelopsis, the second- However, many are so variable that they cannot ary photophores are so large, and the primary pho- be used to define evolutionary lines. The presence tophores so small, that the pattern of the primary or absence of particular bones is limited to two photophores is obscured. Contrary to the report elements, the supramaxilla and extrascapulars, and of Fraser-Brunner (1949), I am unable to distin- the variation described is limited to changes in guish the primary photophores on my examples of shape, size, position, and sculpturing of individual Scopelopsis. bones that are invariably present. The following classification uses both osteological characters and THE EVOLUTIONARY LINEAGES patterns of photophores and luminescent tissue. A Evolution within the family Myctophidae has classification based upon features of two presum- resulted in a radiation of species within a number ably unrelated morphologic systems should be more of evolutionary lines. During the course of this informative than one based upon either system radiation, changes have occurred in the morphol- alone. The larval features of myctophids described ogy of the various groups, as well as in the pat- by Moser and Ahlstrom (1970) were published terns of photophores and luminous tissue. The after the present study was completed and are not similarities and differences in osteology and photo- included in the diagnoses below; their findings are phore patterns closely parallel one another and discussed in the section on relationships. allow recognition of various evolutionary lineages The taxonomic categories recognized below in- within the family. The formal taxonomic categories clude two subfamilies, five tribes, and 28 genera. within the family are defined below on the basis of osteology and photophore pattern. Subfamily Myctophinae Fowler, 1925 The geographic distribution of the family is extensive; lanternfishes occur in all major oceans Definition: (1) C04 orbital shelf extensive; from at least 80° North to 70° South. Most of the (2) jaws short or moderate in length, extending taxa described below also have extended ranges. one-half eye diameter or less behind posterior mar- If no mention is made of distribution, the particu- gin of orbit; (3) preopercular flag absent or free lar taxon is found in the Pacific, Atlantic, and from dorsal tip of preopercle; (4) metapterygoid Indian oceans. The approximate ranges of those strut usually lateral to body of metapterygoid; few taxa with restricted distributions are listed. (5) first pharyngobranchial with none, one, or two Any discussion regarding the validity of a par- tooth plates; (6) dorsal and ventral extrascapulars ticular taxon is unfortunately a subjective evalu- separate or only ventral extrascapular present ation, based upon the available evidence and the (7) posteromedial shelf on cleithrum absent; (8) 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 41

TABLE 11 CHARACTERS OF THE PHOTOPHORES (See text for explanation of characters)

PO Cheek Photophores Secondary Photophores Elevated VO Number of Prc Number of VO Number of Pol GENERA Elevated Angle of PVO Protomyctophum V 4 0 2 0 Hierops V 4 0 2 0 Electrona A V 4 0 2 0 Metelectrona A V 4 2 0-2 2 0 Hygophum A 4 2 2 0 Benthosema 4 2 1 2 0 Diogenichthys 4 2 1 2 0 Myctophum A 4 1 2 0 Ctenoscopelus A 4 1 2 0 Symbolophorus A 4 1 2 0 Loweina A 0 2-4 1 2 0 Tarletonbeania A 0 6 1 1 0 Gonichthys A 0 4 1 2 0 Centrobranchus A 0 4 1 2 0 Lobianchia 4 A 5 2; 3 1-2 4 0 Diaphus 4 A 5 2; 3 1-3 4 0 Notolychnus 3; 4? A 4 2 2 2 0 Taaningichthys V V 5-8 1 3 0 Lam padena —‚4 V V 4-6 1 3 0 Lam panyctodes 3; 5 V 5 2; 3 1 5 0 Stenobrachius 4 V V 4-5 1 3-4 0 Triphoturus 4 V V 5 2 2 3 0 Parvilux 4 V V 3-6 2 4 0 Lam panyctus 4 V V 4 —, 2 2 3-4 0-2 LL, + Lepidophanes 4 V V 5-6 2 2 3-4 0 + Ceratoscopelus V V 5 2 4 0 Gymnoscopelus V V 5-6 2 4-9 0 Nasolychnus V 5-6 2 4-6 0 Lam pichthys V 5 3 4 3-7 Not oscopelus V 5 2-3 3-4 0 Hintonia V V 5 2 3 5-6 1 LL Scopelopsis / / /

PVC), ventral to or opposite lower margin of pec- luminous glands usually present and usually sex- toral base; (9) PLO ventral to, opposite, or dorsal ually dimorphic, variable in shape, size, and num- to pectoral base; (10) one or two Prc on or below ber; supracaudal glands usually in males only, lateral line; (11) no cheek photophores; (12) no infracaudal glands usually in females only; (16) secondary photophores; (13) Dn and Vn usually larval eyes elliptical in outline. present; (14) no luminous tissue present on body Content: two tribes, 11 genera, and about 70 other than caudal luminous glands; (15) caudal species. 42 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

Tribe Myctophini Fowler, 1925 Content: five species, type-species Protomycto- phum arcticum (Liitken, 1892). Definition: (1) antorbital not reduced; (2) jaws short, extending one-quarter eye diameter or less Genus Electrona Goode and Bean, 1896 behind posterior margin of orbit; (3) mouth ter- Definition: (1) CO3 posterior plate and lateral (4) basibranchial tooth plate usually not minal; shelf completely fused; (2) premaxillary shelf pres- extending beyond third hypobranchial; (5) pro- ent or absent; (3) maxillary shelf present; (4) pos- (6) PVO current caudal rays not fused at tips; terior ventral expansion of maxillary great; (5) jaw (7) PLO ventral to or dis- horizontal or inclined; teeth small and conical; (6) urohyal wing anterior tinctly dorsal to pectoral base; (8) four VO; (9) to or at anterior margin of second hypobranchial; VO level or VO, elevated; (10) none, one, or two (7) orbital process of hyomandibula slight or Pol; (11) two Prc; (12) caudal luminous glands absent; (8) preopercular process of hyomandibula of variable form. weak or moderate; (9) hypural flange moderate; Content: seven genera, Protomyctophum, Elec- (10) PVO inclined; (11) PLO ventral to pectoral trona, Benthosema, Diogenichthys, Hygophum, base; (12) VO level or VO, elevated; (13) SAO Myctophum, and Symbolophorus, and about 55 strongly or weakly angled, SAO, variable in posi- species; type-genus Myctophum Rafinesque. tion; (14) none, one, or two Pol; (15) Dn and Vn (or SO) present; (16) supracaudal luminous Genus Protomyctophum Fraser-Brunner, 1949 glands either a series of small, non-overlapping organs with pigmented borders, or one or two small Definition: (1) CO3 posterior plate and lateral organs without marginal pigment. shelf completely fused; (2) premaxillary shelf pres- Content: six or seven species; type-species Elec- ent; (3) maxillary shelf absent; (4) posterior ven- trona rissoi (Cocco, 1829). tral expansion of maxillary great; (5) jaw teeth Synonyms: Elampa Fraser-Brunner, 1949; small and conical; (6) urohyal wing posterior to Elampadena Whitley, 1953; Metelectrona Wisner, anterior margin of second hypobranchial; (7) 1963. orbital process of hyomandibula slight or absent; (8) preopercular process of hyomandibula weak; Genus Benthosema Goode and Bean, 1896 (9) hypural flange moderate; (10) PVO horizon- Definition: (1) CO3 posterior plate and lateral tal; (11) PLO ventral to pectoral base; (12) VO shelf completely or partially fused; (2) no premax- level; (13) SAO straight or weakly angled, SAO, illary shelf; (3) maxillary shelf present or absent; variable in position; (14) no Pol; (15) Dn present (4) posterior ventral expansion of maxillary great; or absent; Vn present; (16) supracaudal luminous (5) jaw teeth small and conical; (6) urohyal wing glands variable: a small or large, single organ with at anterior margin of second hypobranchial; (7) or without marginal pigment, or a series of non- orbital process of hyomandibula slight or absent; overlapping organs with marginal pigment. (8) preopercular process of hyomandibula moder- Content: ten species; type-species Protomycto- ate; (9) hypural flange moderate or well developed; phum tenisoni (Norman, 1930). (10) PVO horizontal; (11) PLO dorsal to pec- toral base; (12) VO elevated; (13) SAO moder- Protomyctophum Fraser-Brunner, 1949 2 Subgenus ately or strongly angled, SAO, variable in position; Definition: (1) frontals between orbits wider (14) one Pol; (15) Dn present or absent, Vn (or than posterior portion of maxillary; (2) eyes nor- SO) present; (16) supracaudal luminous glands mal in position; (3) supracaudal luminous glands variable: a small or large, single organ with or variable, but never a large, single organ bordered without marginal pigment, or a series of non- by heavy black pigment. overlapping organs with marginal pigment. Content: seven species. Content: five or six species; type-species Bentho- sema glaciale (Reinhardt, 1837). Subgenus Hierops Fraser-Brunner, 1949 Genus Diogenichthys Bolin, 1939 Definition: (1) frontals between orbits usually Definition: (1) CO3 posterior plate and lateral narrower than posterior portion of maxillary, shelf completely fused; (2) no premaxillary shelf; rarely the same width; (2) eyes often displaced (3) no maxillary shelf; (4) posterior ventral expan- dorsally as "semi-telescopic" organs; (3) supra- sion of maxillary moderate; (5) anterior teeth of caudal luminous glands as a large single organ premaxillary flattened, posterior teeth of premaxil- bordered by heavy black pigment. lary weakly hooked, outer row of anterior teeth of 1972 OSTEOLOGY AND RELATIO NSHIPS OF LANTERNFISHES 43 dentary greatly widened, posterior teeth of dentary Synonyms: Scopelus Cuvier, 1817; Dasyscope- strongly hooked; (6) urohyal wing anterior to lus Gunther, 1864; Stylopthalmoides Mazzarelli, anterior margin of second hypobranchial; (7) 1912 ( in part); Ctenoscopelus Fraser-Brunner, orbital process of hyomandibula well developed; 1949. (8) preopercular process of hyomandibula weak or moderate; (9) hypural flange well developed; Genus Symbolophorus Bolin and Wisner in (10) PVO horizontal; (11) PLO dorsal to pec- Bolin, 1959 toral base; (12) VO, elevated; (13) SAO in a Definition: (1) CO3 posterior plate and lateral straight line or weak angle, SAO, behind V03; shelf completely or partially fused; (2) no pre- (14) one Pol; (15) Dn present, often sexually maxillary shelf; (3) maxillary shelf present; (4) dimorphic, no Vn; (16) supracaudal luminous posterior ventral expansion of maxillary moderate; glands in males only, as a large, single organ bor- (5) jaw teeth all small and conical or inner row of dered by heavy black pigment. dentary teeth enlarged; (6) urohyal wing at ante- Content: three species; type-species Diogenich- rior margin of second hypobranchial; (7) orbital thys laternatus (Garman, 1899). process of hyomandibula well developed; (8) pre- opercular process of hyomandibula strong; (9) Genus Hygophum Bolin, 1939 hypural flange well developed; (10) PVO inclined; Definition: (1) CO3 posterior plate and lateral (11) PLO dorsal to pectoral base; (12) VO level; shelf partially fused; (2) no premaxillary shelf; (13) SAO strongly angled, SAO, before V03; (14) (3) maxillary shelf present or absent; (4) posterior one Pol; (15) Dn and Vn present; (16) supracau- ventral expansion of maxillary great; (5) jaw teeth dal luminous glands variable, but never a large, small and conical; (6) urohyal wing at or posterior sing'e organ bordered by heavy black pigment. to anterior margin of second hypobranchial; (7) Content: about ten species (Bolin, 1959); type- orbital process of hyomandibula slight or absent; species Symbolophorus californiensis (Eigenmann (8) preopercular process of hyomandibula moder- and Eigenmann, 1889). ate; (9) hypural flange moderate; (10) PVO Synonym : Stylopthalmoides Mazzarel1 i, 1912 inclined; (11) PLO dorsal to pectoral base; (12) (in part). VO level; (13) SAO strongly or moderately angled; SAO, over or before V0 ; (14) two Pol; (15) Dn 3 Gonichthyini, new tribe and Vn present; (16) supracaudal glands in males only, as a large, single organ bordered by heavy Definition: (1) antorbital reduced; (2) jaws black pigment. moderate in length, extending one-half eye diam- Content: seven or eight species; type-species eter behind posterior margin of orbit; (3) mouth Hygophum hygomi (Liitken, 1892). subterminal, snout projecting; (4) basibranchial tooth plate extending beyond posterior margin of Genus Myctophum Rafinesque, 1810 third hypobranchial; (5) procurrent caudal rays Definition: (1) CO3 posterior plate and lateral weakly fused at tips; (6) PVO inclined; (7) PLO shelf completely or partially fused; (2) no pre- at upper edge of pectoral base or opposite base; maxillary shelf; (3) maxillary shelf present; (4) (8) two to six VO; (9) VO level; (10) one Pol; posterior ventral expansion of maxillary moderate; (11) one or two Prc; (12) infracaudal glands pres- (5) jaw teeth all small and conical, or anterior teeth ent or absent; supracaudal glands present only in of premaxillary slightly recurved; (6) urohyal wing males as a single, large organ without marginal pig- ment, or as a series of small, non-overlapping at or anterior to anterior margin of second hypo- branchial; (7) orbital process of hyomandibula organs bordered by black pigment. slight or well developed; (8) preopercular process Content: four genera, Loweina, Tarletonbeania, of hyomandibula moderate or strong; (9) hypural Gonichthys, and Centrobranchus, and about 12 flange well developed or complex; (10) PVO species; type-genus Gonichthys Gistel. inclined; (11) PLO dorsal to pectoral base; (12) VO level; (13) SAO in a straight or slightly curved Genus Loweina Fowler, 1925 line, SAO, behind V03; (14) one Pol; (15) Dn Definition: (1) CO1 ethmoid process present, and Vn present; (16) supracaudal luminous glands anterior ledge absent; (2) CO3 lateral shelf solid, variable, but never a large, single organ bordered with keel; posterior plate and lateral shelf com- by heavy black pigment. pletely fused; (3) nasal concave with slight ventral Content: about 15 species; type-species Mycto- ledge; (4) posterior dorsal expansion of maxillary phum punctatum Rafinesque, 1810. short; (5) premaxillary teeth small and conical; 44 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 dentary teeth enlarged; (6) preopercular process Genus Gonichthys Gistel, 1850 of hyomandibula strong; (7) ossification between median and opercular heads of hyomandibula mod- Definition: (1) CO1 ethmoid process absent, erate; (8) dorsal margin of symplectic below dorsal anterior ledge present; (2) CO3 lateral shelf solid margin of quadrate; (9) metapterygoid strut lat- or split, with cup; posterior plate and lateral shelf eral to main body of metapterygoid; (10) no basi- partially fused; (3) nasal convex, without ventral hyal ossification; (11) gill rakers lathelike; (12) no ledge; (4) posterior dorsal expansion of maxillary tooth patches on first pharyngobranchial; (13) sec- long; (5) premaxillary teeth moderately hooked; ond epi- and pharyngobranchials not reduced; (14) dentary teeth small and conical; (6) preopercular teeth of third pharyngobranchial unmodified; (15) process of hyomandibula moderate; (7) ossifica- coracoid fenestra present; (16) only ventral extra- tion between medial and opercular heads of hyo- scapular present; (17) seven ossified distal pectoral mandibula extensive; (8) symplectic extending to radials; (18) pelvic radials fused into two single dorsal margin of quadrate; (9) metapterygoid strut elements; (19) pelvic rays eight, rarely nine; (20) lateral to main body of metapterygoid; (10) no hypurals three dorsal plus two ventral; (21) hypu- basihyal ossification; (11) gill rakers lathelike; ral flange well developed; (22) two to four VO; (12) no tooth patches on first pharyngobranchial; (23) SAO in a straight or slightly curved line; (24) (13) second epi- and pharyngobranchials reduced; two Prc; (25) no infracaudal luminous glands; (14) teeth of third pharyngobranchial modified as supracaudal luminous glands present in males only pegs; (15) coracoid fenestra present; (16) dorsal as a large, single organ without marginal pigment. and ventral extrascapulars present; (17) no ossified Contents: four? species; type-species Loweina distal pectoral radials; (18) pelvic radials fused rara (Liitken, 1892). into two single elements; (19) pelvic rays seven or eight; (20) hypurals two dorsal plus one ventral; Genus Tarletonbeania Eigenmann and (21) hypural flange complex; (22) four VO; (23) Eigenmann, 1890 SAO strongly angled; (24) two Prc; (25) infra- Definition: (1) CO1 ethmoid process present, caudal glands in females only, as a series of small, anterior ledge absent; (2) CO3 lateral shelf split, round, non-overlapping organs; supracaudal lumi- with keel; posterior plate and lateral shelf com- nous glands present in males only, as a series of pletely fused; (3) nasal concave with slight ventral small, round non-overlapping organs bordered by ledge; (4) posterior dorsal expansion of maxillary black pigment. long; (5) jaw teeth small and conical; (6) pre- Content: four species; type-species Gonichthys opercular process of hyomandibula strong; (7) coccoi (Cocco, 1829 ) . ossification between median and opercular heads Synonyms: Alysia Lowe, 1839; Rhinoscopelus of hyomandibula extensive; (8) dorsal margin of Liitken, 1892. symplectic below dorsal margin of quadrate; (9) metapterygoid strut lateral to main body of meta- Genus Centrobranchus Fowler, 1904 pterygoid; (10) slight ossification in basihyal; (11) gill rakers lathelike; (12) one tooth patch on first Definition: (1) CO1 ethmoid process absent, pharyngobranchial; (13) second epi- and pharyn- anterior ledge present; (2) CO3 lateral shelf solid, gobranchials not reduced; (14) teeth of third with keel; lateral shelf and posterior plate par- pharyngobranchial unmodified; (15) coracoid tially fused; (3) nasal convex, without ventral fenestra ossified; (16) dorsal and ventral extra- ledge; (4) posterior dorsal expansion of maxillary scapulars present; (17) no ossified distal pectoral absent; (5) premaxillary teeth moderately or radials; (18) pelvic radials separate as two pairs; strongly hooked; dentary teeth small and conical; (19) pelvic rays eight; (20) hypurals three dorsal (6) preopercular process of hyomandibula strong; plus two ventral; (21) hypural flange complex; (7) ossification between median and opercular (22) six VO; (23) SAO in a straight or slightly heads of hyomandibula extensive; (8) dorsal mar- curved line; (24) one Prc; (25) infracaudal glands gin of symplectic below dorsal margin of quadrate; absent in females, absent or present in males as a (9) metapterygoid strut dorsal to main body of long, single organ with no marginal pigment; metapterygoid; (10) no basihyal ossification; (11) supracaudal glands present in males only as a sin- gill rakers reduced to small patches of tiny teeth; gle, long organ without marginal pigment. (12) no tooth patches on first pharyngobranchial; Content: one or two species; type-species Tarle- (13) second epi- and pharyngobranchials reduced; tonbeania crenularis (Jordan and Gilbert, 1880); (14) teeth of third pharyngobranchial modified as north Pacific Ocean. plates; (15) coracoid fenestra present; (16) dor- 1972 OSTEOLOGY AND RELATIO NSHIPS OF LANTERNFISHES 45 sal and ventral extrascapulars present; (17) two rays; (14) 28 to 30 vertebrae; (15) three epurals; or three ossified distal pectoral radials; (18) pelvic (16) seven dorsal procurrent rays; (17) seven radials fused into two single elements; (19) pelvic ventral procurrent rays; (18) P03 and probably rays eight; (20) hypurals one dorsal and one ven- PO, elevated; (19) PVO inclined; (20) four VO; tral; (21) hypural flange complex; (22) four VO; (21) VO, elevated; (22) two Prc; (23) four pho- (23) SAO in a straight or slightly curved line; tophores far above lateral line; (24) no cheek (24) two Prc; (25) infracaudal luminous glands photophores; (25) no secondary photophores; (26) present in females only, as a series of small, round, Dn present, no Vn; (27) no infracaudal luminous non-overlapping organs; supracaudal luminous glands; supracaudal luminous glands single, large, glands present in males only, as a series of small, bordered by heavy black pigment, larger in males round, non-overlapping organs bordered by black than females; (28) larval eye semielliptical in pigment. outline. Content: four species; type-species Centrobran- Content: one genus and one species. chus choerocephalus Fowler, 1904. Genus Notolychnus Fraser-Brunner, 1949 Lampanyctinae, new subfamily Definition: as for the tribe. Content: one species, Notolychnus valdiviae Definition: (1) C04 orbital shelf usually moder- (Brauer, 1904). ate, rarely extensive, or circumorbitals unossified; Synonym: Vestula Bolin, 1946. (2) jaws usually long, extending one or more eye diameters behind posterior margin of orbit, rarely Lampanyctini, new tribe short or moderate; (3) preopercular flag absent or fused to dorsal tip of preopercle; (4) meta- Definition: (1) extrascapulars ossified, circum- pterygoid strut usually dorsal to main body of me- orbitals usually ossified; CO3 lateral shelf usually tapterygoid; (5) first pharynobranchial with none concave, rarely curved, never with keel or ridge; to six tooth plates; (6) dorsal and ventral extra- (2) no supramaxillary; (3) posterior teeth of den- scapulars fused into one element, or extrascapulars tary moderately or strongly hooked; (4) postpala- unossified; (7) posteromedial shelf on cleithrum tine process and dorsal wing of palatine ossified; usually present; (8) PVC', ventral to, opposite, or (5) mesopterygoid extending forward to anterior dorsal to pectoral base; (9) PLO dorsal to pectoral one-quarter of palatine; (6) preopercular flag base; (10) usually three to nine Prc, rarely two; absent or fused to preopercular tip; (7) usually no if two, one high above lateral line; (11) cheek foramen in ceratohyal of adults; (8) posteromedial photophores present or absent; (12) secondary shelf on cleithrum present; (9) ossified distal pec- photophores present or absent; (13) Dn present toral radials none or ten; (10) pubic plate of or absent, Vn usually present; (14) luminous tis- pelvic bones weakly ossified; (11) ischial ligament sue other than caudal glands present or absent; moderate or long, directed medially or posteriorly; (15) caudal luminous glands usually present and (12) eight pelvic rays; (13) 12 to 16 dorsal rays; rarely sexually dimorphic, variable in form; (16) (14) 31 to 40 vertebrae; (15) usually three epu- eyes of larvae round or semielliptical in outline. rals, rarely two; (16) five to ten dorsal procurrent Content: four tribes, 17 genera, and about 130 rays; (17) six to ten ventral procurrent rays; (18) species. PO level or PO, elevated; (19) PVO vertical; (20) three to eight VO; (21) VO level, or VO, ele- Notolychnini, new tribe vated, or VO, and V03 elevated; (22) three or four Prc; (23) no photophores far above lateral Definition: (1) circumorbitals and extrascapulars line; (24) cheek photophores present or absent; unossified; (2) no supramaxillary; (3) posterior (25) secondary photophores present or absent; pri- teeth of dentary small and conical; (4) postpalatine mary photophores always distinct; (26) Vn pres- process and dorsal wing of palatine unossified; (5) ent, no Dn; (27) both supracaudal and infracaudal mesopterygoid extending forward only to posterior luminous glands present, not sexually dimorphic; one-third of palatine; (6) no preopercular flag; (28) larval eyes round in outline. (7) foramen in ceratohyal of adults; (8) no pos- Content: eight genera, Taaningichthys, Lampa- teromedial shelf on cleithrum; (9) no ossified dis- dena, Bolinichthys, Lepidophanes, Ceratoscopelus, tal pectoral radials; (10) pubic plate of pelvic Stenobrachius, Lampanyctus, and Triphoturus, bones weakly ossified; (11) ischial ligament and about 60 species; type-genus Lampanyctus obscure; (12) six pelvic rays; (13) eleven dorsal Bonaparte. 46 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No.13

Genus Taaningichthys Bolin, 1959 foramen large; (13) anterior tip of urohyal with Definition: (1) CO3 lateral shelf perpendicular, two heads; (14) urohyal wing at anterior margin solid, without keel; anterior lateral shelf and plate of second hypobranchial; (15) basibranchial plate equal; (2) C04 orbital shelf moderate; (3) C05 extends behind third hypobranchial; (16) first straight; (4) jaws moderate, extending one-half eye pharyngobranchial with one tooth plate; (17) no diameter behind posterior margin of orbit; (5) ossified distal pectoral radials; (18) ischial liga- anterior portion of premaxillary with enlarged ment moderate, directed medially; (19) origin of dentigerous area; (6) posterior dorsal expansion first epural over anterior part of terminal vertebra; of maxillary short; (7) anterior teeth of dentary (20) hypural flange moderate; (21) procurrent small and conical or moderately hooked; posterior rays strongly fused, without posterior spines; (22) portion of dentary with a row of strongly hooked PO level or PO, elevated; (23) four to six VO; teeth; (8) no posterior expansion on dentary; (9) (24) VO level; (25) one Pol; (26) three Prc; (27) hyomandibular nerve foramen between first two no secondary photophores; (28) supra- and infra- hyomandibular heads; (10) preopercular process caudal luminous glands large, single organs of of hyomandibula moderate; (11) opercular head translucent material bordered by heavy black pig- of hyomandibula without dorsal process; (12) ment; (29) no luminous tissue on body other than quadrate foramen small or large; (13) anterior tip caudal glands and possibly eyes. of urohyal slightly split or with two heads; (14) Content: ten species; type-species Lam padena urohyal wing at anterior margin of second hypo- speculigera Goode and Bean, 1896. branchial; (15) basibranchial plate not extending Synonym: Lychnophora Fraser-Brunner, 1949. beyond third hypobranchial; (16) first pharyngo- branchial with one tooth plate; (17) no ossified Bolinichthys, new genus distal pectoral radials; (18) ischial ligament short or moderate, directed medially; (19) origin of first Definition: (1) CO3 lateral shelf perpendicular, epural over anterior part of terminal vertebra; (20) solid, without keel; anterior lateral shelf and plate hypural flange moderate or well developed; (21) equal; (2) C04 orbital shelf extensive; (3) C05 procurrent caudal rays not fused at tips, without straight; (4) jaws short or moderate, extending posterior spines; (22) PO level; (23) five to eight one-half eye diameter or less behind posterior mar- VO; (24) VO level; (25) one Pol; (26) three Prc; gin of orbit; (5) anterior portion of premaxillary (27) no secondary photophores; (28) supra- and with enlarged dentigerous area; (6) posterior dor- infracaudal luminous glands large, single organs of sal expansion of maxillary long; (7) anterior teeth translucent material bordered by heavy black pig- of dentary small and conical; posterior portion of ment; (29) no luminous tissue on body other than dentary with row of moderately hooked teeth; (8) caudal glands and possibly eyes. no posterior expansion on dentary; (9) hyoman- Content: three species; type-species Taaningich- dibular nerve foramen in anterior hyomandibular thys bathyphilus (Taaning, 1928). head; (10) preopercular process of hyomandibula strong; (11) opercular head of hyomandibula without dorsal process; (12) quadrate foramen Genus Lam padena Goode and Bean in Gill, 1893. small; (13) anterior tip of urohyal with one head; (14) urohyal wing at anterior margin of second Definition: (1) CO3 lateral shelf perpendicular, hypobranchial; (15) basibranchial plate not extend- split, with keel; anterior lateral shelf and plate ing beyond third hypobranchial; (16) first pha- equal; (2) C04 orbital shelf extensive; (3) C05 ryngobranchial with one or two tooth plates; (17) curved; (4) jaws long, extending one eye diameter ten ossified distal pectoral radials; (18) ischial or more behind posterior margin of orbit; (5) ligament moderate and directed posteromedially; anterior portion of premaxillary with enlarged (19) origin of first epural over anterior part of dentigerous area; (6) posterior dorsal expansion terminal vertebra; (20) hypural flange moderate; of maxillary short; (7) anterior teeth of dentary (21) procurrent caudal rays strongly fused at tips, enlarged; posterior portion of dentary with row without posterior spines; (22) PO, elevated; (23) of strongly hooked teeth; (8) posterior portion of five VO; (24) V02 elevated; (25) two Pol; (26) dentary with small dorsal expansion; (9) hyoman- three Prc; (27) secondary photophores present or dibular nerve foramen between first two hyo- absent on head and body; (28) supra- and infra- mandibular heads; (10) preopercular process of caudal luminous glands of narrow, overlapping hyomandibula strong; (11) opercular head of hyo- plates with indistinct divisions unmarked by pig- mandibula without dorsal process; (12) quadrate ment; (29) luminous tissue often at bases of dor- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 47 sal, anal, pectoral, and ventral fins, on dorsal sur- equal; (2) C04 orbital shelf moderate; (3) C05 face of head and possibly on eyes. straight; (4) jaws moderate, extending one-half Content: five to seven species; type-species eye diameter behind posterior margin of orbit; (5) Bolinichthys longipes (Brauer, 1906). B. longipes, anterior portion of premaxillary without enlarged B. photothorax, B. indicus, B. blacki, and B. supra- dentigerous area; (6) posterior dorsal expansion lateralis can be referred to the new genus. I take of maxillary long; (7) anterior teeth of dentary great pleasure in naming the genus after Professor small and conical; posterior portion of dentary with Rolf Bolin of Hopkins Marine Station, who has row of moderately hooked teeth; (8) no posterior given me much advice and encouragement. expansion on dentary; (9) hyomandibular nerve foramen in anterior hyomandibular head; (10) Genus Lepidophanes Fraser-Brunner, 1949 preopercular process of hyomandibula strong; (11) opercular head of hyomandibula without dorsal Definition: (1) CO3 lateral shelf strongly con- process; (12) quadrate foramen small; (13) ante- cave, solid, with keel; anterior lateral shelf and rior tip of urohyal slightly split or with two heads; plate equal; (2) C04 orbital shelf moderate; (3) (14) urohyal wing at anterior margin of second C05 straight; (4) jaws long, extending one or more hypobranchial; (15) basibranchial plate not extend- eye diameters behind posterior margin of orbit; (5) ing beyond third hypobranchial; (16) first pha- anterior portion of premaxillary without enlarged ryngobranchial with one tooth plate; (17) no dentigerous area; (6) posterior dorsal expansion ossified distal pectoral radials; (18) ischial liga- of maxillary long; (7) anterior teeth of dentary ment moderate and directed posteromedially; (19) small and conical; posterior portion of dentary with origin of first epural over anterior part of terminal row of moderately hooked teeth; (8) no posterior vertebra; (20) hypural flange well developed; (21) expansion on dentary; (9) hyomandibular nerve procurrent caudal rays strongly fused, with strong foramen in anterior hyomandibular head; (10) posterior spines on ventral series and moderate preopercular process of hyomandibula strong; (11) posterior spines on dorsal series; (22) PO level; head of hyomandibula with small dorsal opercular (23) five VO; (24) VO level; (25) two Pol; (26) process; (12) quadrate foramen small; (13) ante- four Prc; (27) no secondary photophores; (28) rior tip of urohyal with two heads; (14) urohyal supra- and infracaudal luminous glands of nar- wing at anterior margin of second hypobranchial; row, overlapping plates with indistinct divisions (15) basibranchial plate not extending beyond unmarked by pigment; (29) luminous tissue at third first hypobranchial; (16) pharyngobranchial bases of anal and pelvic fins, before and behind with three tooth plates; (17) ten ossified distal dorsal fin and between the first PO photophores, pectoral radials; (18) ischial ligament long and on dorsal surface of head in some species. directed posteriorly; origin of first (19) epural Content: three species; type-species Cerato- over or behind posterior margin of terminal ver- scopelus maderensis (Lowe, 1839). tebra; (20) hypural flange moderate; (21) pro- current rays strongly fused with moderate poste- rior spines on ventral series; (22) PO, elevated; Genus Stenobrachius Eigenmann and (23) five or six VO; (24) V02 elevated; (25) two Eigenmann, 1890 Pol; (26) four Prc; (27) no secondary photo- lateral shelf strongly con- phores; (28) supra- and infracaudal luminous Definition: (1) CO3 glands of narrow, overlapping plates with indis- cave, solid, with cup; anterior lateral shelf and tinct divisions unmarked by pigment; (29) lumi- plate equal; (2) CO4 orbital shelf moderate; (3) jaws long, extending one eye nous tissue at bases of dorsal, anal, pectoral, and C05 straight; (4) adipose fins. diameter or more behind posterior margin of premaxillary without Content: two species; type-species Lepidophanes orbit; (5) anterior portion of guentheri Goode and Bean, 1896; north Atlantic enlarged dentigerous area; (6) posterior dorsal (7) anterior teeth Ocean. As here restricted, the genus includes only expansion of maxillary short; of small and conical; posterior portion of the type-species and L. gaussi; other species previ- dentary ously referred to Lepidophanes are placed in the dentary with row of moderately hooked teeth; (8) no posterior expansion on genus Bolinichthys. dentary; (9) hyoman- dibular nerve foramen between first two hyo- Genus Ceratoscopelus Gunther, 1864 mandibular heads; (10) preopercular process of hyomandibula moderate or strong; (11) opercular Definition: (1) CO3 lateral shelf perpendicular, head of hyomandibula with or without small dor- solid, with keel; anterior lateral shelf and plate sal process; (12) quadrate foramen large; (13) 48 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. I3 anterior tip of urohyal with two heads; (14) uro- by pigment; (29) luminous tissue present or absent hyal wing at anterior margin of second hypo- at base of adipose fin; no other luminous tissue on branchial; (15) basibranchial plate not extending body other than caudal glands. beyond third hypobranchial; (16) first pharyngo- Contents: about 40 species; type-species Lam- branchial with one tooth plate; (17) no ossified panyctus crocodilus (Risso, 1810). distal pectoral radials; (18) ischial ligament mod- Synonyms: Nannobrachium Gunther, 1887; Pro- erate or long, directed posteromedially; (19) ori- macheon Weber, 1913; Nyctimaster Jordan, 1921; gin of first epural over anterior part of terminal Serpa Whitley, 1933; Parvilux Hubbs and Wisner, vertebra; (20) hypural flange moderate; (21) pro- 1964. current caudal rays strongly fused, without poste- rior spines; (22) PO, elevated; (23) four or five Genus Triphoturus Fraser-Brunner, 1949 VO; (24) VO level; (25) one Pol; (26) three or four Prc; (27) no secondary photophores; (28) Definition: (1) CO3 lateral shelf and plate supra- and infracaudal luminous glands of nar- poorly ossified, weakly concave, with keel; (2) C04 row, overlapping plates with indistinct divisions orbital shelf moderate; (3) C05 straight; (4) jaws unmarked by pigment; (29) no luminous tissue on long, extending one eye diameter or more behind body other than caudal glands. posterior margin of orbit; (5) anterior portion of Content: two species; type-species Stenobrachius premaxillary without enlarged dentigerous area; leucopsarus Eigenmann and Eigenmann, 1890; (6) posterior dorsal expansion of maxillary short; north Pacific Ocean. (7) anterior teeth of dentary small and conical; posterior portion of dentary with row of moderately Genus Lampanyctus Bonaparte, 1840 or strongly hooked teeth; (8) posterior dorsal ex- Definition: (1) CO3 lateral shelf usually strongly pansion present on dentary; (9) hyomandibular concave, rarely perpendicular, solid, with keel; nerve foramen between first two hyomandibular anterior lateral shelf extends forward beyond plate; heads; (10) preopercular process of hyomandibula (2) CO4 orbital shelf moderate; (3) C05 straight; moderate; (11) opercular head of hyomandibula (4) jaws long, extending one eye diameter or more without dorsal process; (12) quadrate foramen behind posterior margin of orbit; (5) anterior small; (13) anterior tip of urohyal with two heads; portion of premaxillary without expanded dentig- (14) urohyal wing posterior to anterior margin of erous area; (6) posterior dorsal expansion of max- second hypobranchial; (15) basibranchial plate be- illary short; (7) anterior teeth of dentary small fore or behind posterior margin of third hypo- and conical; posterior portion of dentary with branchial; (16) first pharyngobranchial with one row of moderately hooked teeth; (8) posterior tooth plate; (17) no ossified distal pectoral radials; dorsal expansion present on dentary; (9) hyoman- (18) ischial ligament long, directed posteriorly; dibular nerve foramen between first two hyo- (19) origin of first epural over anterior part of mandibular heads; (10) preopercular process of terminal vertebra; (20) hypural flange moderate; hyomandibula moderate; (11) opercular head (21) procurrent rays strongly fused at tips, with- of hyomandibula with small dorsal process; (12) out posterior spines; (22) PO, elevated; (23) five quadrate foramen large or small; (13) anterior VO; (24) VO, and V03 elevated; (25) two Pol; tip of urohyal with two heads; (14) urohyal wing (26) three Prc; (27) no secondary photophores; posterior to anterior margin of second hypobran- (28) supra- and infracaudal luminous glands of chial; (15) basibranchial plate not extending narrow, overlapping plates with indistinct divisions beyond third hypobranchial; (16) first pharyngo- unmarked by pigment; (29) no luminous tissue on branchial with one or two tooth plates; (17) no body other than caudal glands. ossified distal pectoral radials; (18) ischial liga- Content: three? species; type-species Triphoturus ment long, directed posteriorly; (19) origin of first micropterus (Brauer, 1906). epural over anterior part of terminal vertebra; (20) hypural flange moderate; (21) procurrent rays Diaphini, new tribe strongly fused at tips, without posterior spines; (22) PO, elevated; (23) three to six VO, usually Definition: (1) Circumorbitals and extrascapu- four; (24) VO level, arched, or VO, elevated; lars ossified; CO3 lateral shelf usually perpendic- (25) two Pol; (26) three or four Prc; (27) sec- ular, rarely concave; C05 usually curved, rarely ondary photophores present or absent; (28) supra- straight, usually with keel or ridge; (2) no supra- and infracaudal luminous glands of narrow, over- maxillary; (3) posterior teeth of dentary small and lapping plates with indistinct divisions unmarked conical or enlarged; (4) postpalatine process and 50 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

PV02 ventral to or opposite pectoral base; (23) anteriorly beyond plate; (2) C05 curved with keel VO, and VO, elevated; (24) first A0a not ele- or ridge; (3) posterior dorsal expansion of maxil- vated; (25) one Pol; (26) five Prc; (27) no cheek lary short; (4) supramaxillary small and L-shaped; photophores; (28) supra- and infracaudal lumi- (5) anterior part of premaxillary with expanded nous glands present in all adults as few overlap- dentigerous area; (6) anterior teeth of dentary ping plates with indistinct divisions unmarked by small and conical; posterior part of dentary with pigment; (29) luminous tissue at base of dorsal, inner row of enlarged teeth and row of slightly anal, pectoral, and pelvic fins, before and behind hooked teeth; (7) no posterior expansion on den- dorsal fin and on dorsal surface of head. tary; (8) hyomandibular nerve foramen in first Content: one species, Lampanyctodes hectoris hyomandibular head; (9) opercular head of hyo- (Glinther, 1876); south Pacific and Indian oceans. mandibula with dorsal process; (10) anterior tip of urohyal with two heads; (11) urohyal wing at Genus Gymnoscopelus Gunther, 1873 anterior margin of second hypobranchial; (12) Definition: (1) CO3 anterolateral shelf and basibranchial plate not extending beyond third plate equal or shelf projecting anteriorly beyond hypobranchial; (13) pubic plate of pelvic bones plate; (2) C05 curved or straight, with keel or weakly or moderately ossified; (14) 22 to 26 dor- ridge; (3) posterior dorsal expansion of maxillary sal rays; (15) 19 to 20 anal rays; (16) 37 verte- short; (4) supramaxillary small and L-shaped; (5) brae; (17) origin of first epural over or behind anterior part of premaxillary without expanded posterior margin of terminal vertebra; (18) hypu- dentigerous area; (6) dentary teeth small and coni- ral flange well developed; (19) no secondary pho- cal; (7) no posterior expansion on dentary; (8) tophores; (20) PO level; (21) PVO vertical; (22) hyomandibular nerve foramen in first or between PVC), dorsal to pectoral base; (23) VO level; (24) first two hyomandibular heads; (9) opercular head first A0a not elevated; (25) usually two Pol, rarely of hyomandibula with or without dorsal process; three, in a horizontal line; (26) three or four Prc; (10) anterior tip of urohyal slightly split or with (27) no cheek photophores; (28) infracaudal two heads; (11) urohyal wing anterior to, at, or luminous glands small, without pigment in all posterior to anterior margin of second hypo- adults; supracaudal luminous glands small, without branchial; (12) basibranchial plate not extending pigment in females, large single organ bordered by beyond third hypobranchial; (13) pubic plate of heavy black pigment in males; (29) luminous tis- pelvic bones weakly ossified; (14) 16 to 21 dorsal sue near bases of pectoral and pelvic fins and at rays; (15) 17 to 22 anal rays; (16) 41 to 45 verte- anterior portion of anal fin. brae; (17) origin of first epural over or behind ter- Content: six species; type-species Notoscopelus minal vertebra; (18) hypural flange moderate; resplendens (Richardson, 1844). (19) no secondary photophores; (20) PO level; Synonym: Catablemella Eigenmann and Eigen- (21) PVO vertical; (22) PVC), opposite or dorsal mann, 1890. to pectoral base; (23) VO level; (24) first A0a highly elevated; (25) two Pol in ascending line; Genus Lampichthys Fraser-Brunner, 1949 (26) four to nine Prc; (27) no cheek photophores; Definition: (1) CO3 anterolateral NH and (28) no caudal luminous glands; (29) luminous plate equal; (2) C05 straight, with keel 9r ridge; tissue scattered on body near bases of pectoral and (3) posterior dorsal expansion of maxil›-iry short; pelvic fins and above anterior lateral line. (4) supramaxillary small and L-shaped; (5) ante- Content: two subgenera and nine species; type- rior part of premaxillary withouVe"xpanded den- species Gymnoscopelus aphya Gunther, 1873; tigerous area; (6) dentary Ikefh-s-mall and conical; southern hemisphere. (7) no posterior exipavAion on dentary; (8) hyo- Subgenus Gymnoscopelus Gunther, 1873 mandibular nerve -foramen in first hyomandibular Definition: (1) PVC), opposite pectoral base. he; (9) opercular head of hyomandibula with Content: four species. dorsal process; (10) anterior tip of urohyal with Subgenus Nasolychnus Smith, 1933 two heads; (11) urohyal wing posterior to anterior Definition: (1) PVC), dorsal to pectoral vase. margin of second hypobranchial; (12) basibran- Content: five species, including tlifree unde- chial plate not extending beyond third hypobran- scribed; type-species GymnosOiyelus fraseri chial; (13) pubic plate of pelvic bones weakly ossi- (Fraser-Brunner, 1931). fied; (14) 16 to 17 dorsal rays; (15) 22 anal rays; (16) 41 vertebrae; (17) origin of first epural over Genus Notoscopelus Gtioither, 1864 or behind posterior margin of terminal vertebra; Definition: (1) CO3 latera!1 shelf projecting (18) hypural flange moderate; (19) secondary 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 49

dorsal wing of palatine ossified; (5) mesopterygoid ossified; CO3 lateral shelf perpendicular; C05 usu- extending forward to anterior one-quarter of pala- ally curved and usually with keel or ridge; (2) su- tine; (6) preopercular flag absent or fused to dor- pramaxillary usually present as small, L-shaped sal tip of preopercle; (7) no foramen in anterior element, rarely reduced or absent; (3) posterior ceratohyal of adults; (8) posteromedial shelf on teeth of dentary small and conical, enlarged, or cleithrum present; (9) one to seven ossified distal slightly hooked; (4) postpalatine process and dor- pectoral radials; (10) pubic plate of pelvic bones sal wing of palatine ossified; (5) mesopterygoid widely ossified, meeting in midline; (11) ischial extending forward to anterior one-quarter of pala- ligament short or moderate, directed medially; tine; (6) preopercular flag usually fused to dorsal (12) eight pelvic rays; (13) 12 to 18 dorsal rays; tip of preopercle, rarely absent; (7) no foramen in (14) 32 to 37 vertebrae; (15) two epurals; ceratohyal of adults; (8) posteromedial shelf on (16) five to eight dorsal procurrent rays; (17) five cleithrum present; (9) no ossified distal pectoral to seven ventral procurrent rays; (18) PO4 ele- radials; (10) pubic plate of pelvic bones usually vated; (19) PVO inclined; (20) five VO; (21) VO, weakly ossified, rarely strongly ossified; (11) ischial and VO, elevated; (22) four Prc; (23) no photo- ligament short, directed medially; (12) eight pelvic phores far above lateral line; (24) no check pho- rays; (13) 13 to 26 dorsal rays; (14) 37 to 45 tophores; (25) no secondary photophores; (26) Dn vertebrae; (15) two or three epurals; (16) eight present, Vn present or absent; (27) caudal lumi- to thirteen dorsal procurrent rays; (17) nine to nous glands present or absent; sexually dimorphic fifteen ventral procurrent rays; (18) PO level or if present; (28) larval eyes round in outline. PO, and PO, elevated; (19) PVO horizontal or Content: two genera, Lobianchia and Diaphus, vertical; (20) five or six VO; (21) VO level, or and about 50 species; type-genus Diaphus Eigen- V02, or VO, and VO, elevated; (22) three to nine mann and Eigenmann. Prc; (23) no photophores far above lateral line; (24) cheek photophores present or absent; (25) Genus Lobianchia Gatti, 1903 secondary photophores present or absent; if pres- Definition: (1) Dn small, no Vn; (2) supracau- ent, primary photophores distinct or obscure; (26) dal luminous glands in males only, as a series of Dn and Vn present; (27) caudal luminous glands overlapping plates with divisions unmarked by pig- present or absent; if present, rarely sexually dimor- ment; infracaudal luminous glands in females only, phic; (28) larval eyes round in outline. as a series of small, unpigmented non-overlapping Content: six genera, Lampanyctodes, Gymno- organs; (3) no luminous tissue other than caudal scopelus, Notoscopelus, Lampichthys, Scopelopsis, glands on body. and Hintonia, and about 20 species; type-genus Content: two or three species; type-species Lobi- Gymnoscopelus Gunther. anchia gemellari (Cocco, 1838). Synonyms: Pseudodiaphus Taaning, 1918; Hy- Genus Lampanyctodes Fraser-Brunner, 1949 's. perphotops Fraser-Brunner, 1949. Definition: (1) CO3 anterolateral shelf and plate equal; (2) C05 curved, with keel or ridge; Geniis. -atcaphus Eigenmann and Eigenmann, 1890 (3) posterior dorsal expansion of maxillary short; Defiaition: (1) Dn present, Vn usually present; (4) supramaxillary small and L-shaped; (5) ante- both or ns often greatly expanded and sexually rior part of premaxillary without expanded den- dimorphic; (2) no caudal luminous glands; (3) lu- tigerous area; (6) dentary teeth small and conical; minous patch ttsually present above pectoral base (7) no posterior expansion on dentary; (8) hyo- near the PLO phOto-fr&Ore; occasionally numerous mandibular nerve foramen between first two luminous patches over lxidy Associated with other hyomandibular heads; (9) opercular head of hyo- photophores. mandibula without dorsal process; (10) anterior Content: about 50 species (Nafpaktitis, persnal tip of urohyal with two heads; (11) urohyal wing communication); type-species Diaphus theta Ei- at anterior margin of second hypobranchial; (12) genmann and Eigenmann, 1890. bas-ihranchial plate not extending beyond third hy- Synonyms: Aethoprora Goode and Bean, 1896; pobrark,hial; (13) pubic plate of pelvic bones Collettia Goode and Bean, 1896; Panthophos Jor- widely ossifik. d, meeting in midline; (14) 13 to 14 dan and Hubbs, 1925; Lamprossa Jordan and dorsal rays; (1.‘fl 16 to 17 anal rays; (16) 37 to 38 Hubbs, 1925; Cavelampus Whitley, 1933. vertebrae; (17) *origin of first epural over anterior part of terming vertebra; (18) hypural flange Gymnoscopelini, new tribe moderate; (19) Ao secondary photophores; (20) Definition: (1) circumorbitals and extrascapular PO, and PO, elevalted; (21) PVO horizontal; (22) 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 51 photophores present over body and head; primary between first two hyomandibular heads; (9) photophores distinct; (20) PO level; (21) PVO opercular head of hyomandibula without dorsal vertical; (22) PVO, dorsal to pectoral base; (23) process; (10) anterior tip of urohyal slightly split; VO level; (24) first A0a not elevated; (25) three (11) urohyal wing anterior to anterior margin of Pol, forming right angle; (26) four Prc; (27) three second hypobranchial; (12) basibranchial plate to seven primary cheek photophores; (28) supra- extending beyond third hypobranchial; (13) pubic and infracaudal luminous glands small, without plate of pelvic bones weakly ossified; (14) 15 dor- pigment on all adults; (29) luminous tissue on dor- sal rays; (15) 13 to 14 anal rays; (16) 38 to 39 sal surface of head in large specimens, and near vertebrae; (17) origin of first epural over or behind base of pectoral fins. posterior margin of terminal vertebra; (18) hypu- Content: one species (Bolin, personal communi- ral flange moderate; (19) secondary photophores cation), Lampichthys procerus (Brauer, 1904); limited to area of lateral line; primary photophores south Atlantic and south Pacific oceans. distinct; (20) PO level; (21) PVO vertical; (22) PVC), opposite pectoral base; (23) V02 elevated; Genus Scopelopsis Brauer, 1906 (24) first A0a slightly raised; (25) three Pol, in ascending line; (26) five or six Prc; (27) one (1) CO3 Definition: lateral shelf projecting cheek photophore; (28) no caudal luminous anteriorly beyond plate; (2) C05 straight, with glands; (29) luminous tissue at bases of dorsal, ridge or keel; (3) posterior dorsal expansion of anal, and pelvic fins, before and behind dorsal fin maxillary short; (4) supramaxillary small and and on dorsal surface of head. L-shaped; (5) anterior part of premaxillary with- Content: one species, Hintonia candens Fraser- out expanded dentigerous area; (6) anterior teeth Brunner, 1949; south Atlantic and south Pacific of dentary small and conical; posterior part of den- oceans. tary with row of slightly hooked teeth; (7) no pos- terior expansion on dentary; (8) hyomandibular nerve foramen in first hyomandibular head; (9) Key to the Supraspecific Taxa of the opercular head of hyomandibula with small dorsal Family Myctophidae process; (10) anterior tip of urohyal slightly split; (11) urohyal wing at anterior margin of second hypobranchial; (12) basibranchial plate not ex- 1A. No secondary photophores; one or two Prc, tending beyond third hypobranchial; (13) pubic neither far above lateral line; eyes of larvae ellip- plate of pelvic bone weakly ossified; (14) 22 dor- tical; dorsal and ventral extrascapulars separate sal rays; (15) 23 to 24 anal rays; (16) 38 to 39 or only ventral element present; no postero- vertebrae; (17) origin of first epural over anterior medial shelf on cleithrum (SUBFAMILY MYCTOPHINAE) 2 part of terminal vertebra; (18) hypural flange 1B. Secondary photophores present or absent; pri- moderate; (19) secondary photophores present all mary photophores indistinct from secondary over head and body, primary photophores indis- photophores or two to nine Prc; if two Prc, one tinct; (28) supracaudal glands as overlapping far above lateral line; eyes of larvae round or semielliptical; dorsal and ventral extrascapulars plates in males; no caudal luminous glands in fused into one element, or extrascapulars not females; (29) luminous tissue near pectoral base ossified; posteromedial shelf present or absent on and bases of procurrent caudal rays. cleithrum, if absent, extrascapulars not ossified Content: one species, Scopelopsis multipunc- (SUBFAMILY LAMPANYCTINAE) 13 tatus 1906; 2A. PLO ventral to or distinctly dorsal to pectoral Brauer, southern hemisphere. base; jaws short, extending less than one-half eye diameter behind orbit; mouth terminal, Genus Hintonia Fraser-Brunner, 1949 snout not projecting; antorbital not reduced; pro- current caudal rays not fused ...... (TRIBE Definition: (1) CO3 lateral shelf projecting MYCTOPHINI) 3 anteriorly beyond plate (2) C05 curved without 2B. PLO opposite or just dorsal to upper edge of keel or ridge; (3) posterior dorsal expansion of pectoral base; jaws moderate, extending one-half eye diameter behind orbit; mouth subterminal, maxillary long; (4) supramaxillary reduced to snout projecting; antorbital reduced; procurrent small, rectangular remnant or lost; (5) anterior caudal rays weakly fused at tips ...... (TRIBE part of premaxillary without enlarged dentigerous GONICHTHYINI) 10 area; (6) inner row of dentary teeth enlarged; pos- 3A. PLO ventral to pectoral base; A0a and A0p terior part of dentary with row of slightly hooked usually continuous or last one or two A0a ele- vated as Pol photophores 4 teeth; (7) posterior part of dentary with small dor- 3B. PLO dorsal to pectoral base; A0a and A0p dis- sal expansion; (8) hyomandibular nerve foramen continuous, one or two distinct Pol 6 52 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

4A. PVO inclined, in line with P01; maxillary shelf 11A. Two to four VO; two Prc; CO3 lateral shelf present; urohyal wing anterior to or at anterior solid; posterodorsal expansion of maxillary margin of second hypobranchial ...... Electrona short; basihyal unossified; no teeth on first pharyngobranchial; coracoid fenestra present; 4B. PVO horizontal, line through them markedly above PO,; no maxillary shelf; urohyal wing pos- only ventral extrascapular present; seven ossified terior to anterior margin of second hypobran- distal pectoral radials; hypural flange well de- veloped ...... Loweina chial ...... Protomyctophum ...... 5 11B. Six VO; one Prc; CO3 lateral shelf split; postero- 5A. Supracaudal glands variable but never large, dorsal expansion of maxillary long; basihyal single, and bordered by heavy black pigment; with small ossification; one tooth patch on first frontals between orbits not reduced, wider than pharyngobranchial; no coracoid fenestra; dorsal posterior portion of maxillary; eyes normal ...... and ventral extrascapulars present; no ossified ...... subgenus Protomyctophum distal pectoral radials; hypural flange complex 5B. Supracaudal glands of males large, single, and ...... Tarletonbeania bordered by heavy black pigment; frontals 12A. SAO strongly angled; CO3 lateral shelf with between orbits slightly or considerably reduced, cup; posterodorsal expansion of maxillary long; as wide as or narrower than posterior portion of symplectic extending to dorsal margin of quad- maxillary; eyes usually semitelescopic ...... rate; metapterygoid strut lateral to main body of ...... subgenus Hierops bone; gill rakers lathelike; teeth of third pharyn- gobranchial modified as pegs; no ossified distal 6A. PVO horizontal; VO, elevated ...... 7 pectoral radials; hypurals two dorsal plus one 6B. PVO inclined; VO level ...... 8 ventral ...... Gonichthys 12B. SAO in a straight or slightly curved line; CO3 7A. Prc level or Pre, slightly elevated; posteroventral lateral shelf with keel; no posterodorsal expan- expansion of maxillary moderate; orbital process sion on maxillary; symplectic ventral to dorsal of hyomandibula well developed; premaxillary margin of quadrate; metapterygoid strut dorsal teeth flattened, outer row of dentary teeth to main body of bone; gill rakers reduced to widened, posterior portion of dentary with row small patches of tiny teeth; teeth of third pharyn- of strongly hooked teeth ...... Diogenichthys gobranchial modified as plates; two or three ossi- 7B. Pre, highly elevated near lateral line; posteroven- fied distal pectoral radials; hypurals one dorsal tral expansion of maxillary great; orbital process plus one ventral ...... Centrobranchus of hyomandibula slight; premaxillary and den- 13A. No secondary photophores; two Prc; four photo- tary teeth small and conical ...... Benthosema phores far above lateral line, near dorsal pro- 8A. Two Pol; supracaudal luminous glands of males file; only supracaudal luminous gland present as large, single, and bordered by heavy black pig- large, single organ bordered by heavy black pig- ment ...... Hygophum ment; eyes of larvae semi-elliptical; extrascapu- lar(s) unossified; postpalatine process and dorsal 8B. One Pol; supracaudal luminous glands variable wing of palatine unossified; mesopterygoid ex- but never large, single, and bordered by heavy tending forward to posterior one-third of pala- black pigment ...... 9 tine; no posteromedial shelf on cleithrum; six 9A. SAO in a straight or weakly curved line; SA01 pelvic rays; eleven dorsal rays; 28 to 30 verte- behind V03 ...... Myctophum brae ...... (TRIBE NOTOLYCHNINI) ...... Notolychnus 9B. SAO strongly angled; SA01 before V01...... I 3B. Secondary photophores present or absent; pri- ...... Symbolophorus mary photophores indistinct from secondary 10A. PLO opposite pectoral base; females without photophores or three to nine Prc; no primary caudal luminous glands; males with supracaudal photophores far above lateral line; supracaudal glands as a large, single organ, rarely with a gland present or absent, if present as large, single single infracaudal gland; nasal concave with organ bordered by heavy black pigment, a simi- slight ventral ledge; CO1 with ethmoid process lar infracaudal gland also present; eyes of larvae and no anterior ledge; CO3 lateral shelf and pos- round; extrascapular ossified; postpalatine terior plate completely fused; premaxillary teeth process and dorsal wing of palatine ossified; small and conical; second epi- and pharyngo- mesopterygoid extending forward to anterior branchials not reduced; teeth of third pharyngo- quarter of palatine; posteromedial shelf present branchial small and conical; hypurals three on cleithrum: eight pelvic rays; 12 to 26 dorsal dorsal plus two ventral ...... 11 rays; 31 to 45 vertebrae ...... 14 14A. No Dn; posterior portion of dentary with row of 10B. PLO just dorsal to upper edge of pectoral base; moderately or strongly hooked teeth ...... (TRIBE infracaudal (females) and supracaudal (males) LAMPANYCTINI) ...... 15 luminous glands as series of small, nonoverlap- ping organs; nasal convex with no ventral ledge; 14B. Dn present; teeth on posterior portion of dentary CO1 with anterior ledge and no ethmoid process; small and conical, enlarged, or slightly hooked CO3 lateral shelf and posterior plate partially ...... 22 fused; premaxillary teeth moderately or strongly 15A. Supra- and infracaudal luminous glands large, recurved; second epi- and pharyngobranchials single organs bordered by heavy black pigment reduced; teeth of third pharyngobranchial modi- ...... 16 fied as pegs or plates; hypurals one to two dorsal 15B. Supra- and infracaudal luminous glands of nar- plus one ventral ...... 12 row, overlapping plates with no pigment ...... 17 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 53

16A. Luminous tissue on posterior half of iris; CO3 21A. Three to six level VO or four VO with V02 ele- lateral shelf solid, without keel; CO5 straight; vated; opercular head of hyomandibula with jaws moderate, extending one-half eye diameter small dorsal process Lam panyctus behind posterior margin of orbit; posterior por- 218. Five VO with V02 or VO, and VO, elevated; tion of dentary without dorsal expansion; basi- opercular head of hyomandibula without dorsal branchial plate not extending behind third hypo- process Triphoturus branchial; procurrent caudal rays not fused at 22A. No secondary photophores; PO. elevated; PVO tips Taaningichthys inclined, on a line with PO4; no supramaxillary; one to seven ossified distal pectoral radials; ven- 16B. No luminous tissue on posterior half of iris (but tral procurrent rays five to seven (TRIBE rarely on dorsal portion); CO3 lateral shelf split, DIAPHINI) ...... 23 with keel; C05 curved; jaws long, extending one 22B. Secondary photophores present or absent; pri- or more eye diameters behind posterior margin mary photophores indistinct from secondary of orbit; posterior portion of dentary with small photophores, or PO level or P02 and P05 ele- basibranchial dorsal expansion; plate extending vated; PVO horizontal or vertical, not on a line hypobranchial; procurrent behind third caudal with PO4; supramaxillary usually present, rarely rays strongly fused Lam padena reduced or absent; no ossified distal pectoral 17A. Luminous tissue over base of anal fin and on radials; ventral procurrent rays nine to fifteen other portions of body in addition to caudal (TRIBE GYMNOSCOPELINI) ...... 24 luminous glands; hyomandibular nerve foramen 23A. Infracaudal luminous glands in females, supra- in first hyomandibular head; posterodorsal ex- caudal luminous glands in males; no Vn; no pansion of maxillary long 18 luminous patch near pectoral base Lobianchia 17B. Luminous tissue restricted to caudal luminous 23B. No caudal luminous glands; Vn usually present; glands and occasionally at base of adipose fin; luminous patch near pectoral base usually pres- hyomandibular nerve foramen between first two ent Diaphus hyomandibular heads; posterodorsal expansion 24A. Primary photophores indistinct from secondary of maxillary short 20 photophores; 23 to 24 anal rays Scopelopsis IA. Three Prc; luminous tissue on posterior half of 24B. Secondary photophores present or absent, if 13 22 iris; no keel on CO3; orbital shelf of C04 exten- present primary photophores distinct; to 25 sive; enlarged dentigerous area on anterior por- anal rays tion of premaxillary; anterior tip of urohyal with 25A. P02 and P05 elevated; PVO horizontal; VO, and one head; no posterior spines on procurrent cau- VO, slightly elevated; supra- and infracaudal dal rays Bolinichthys luminous glands of moderately wide overlapping plates with no pigment and no sexual dimorph- 188. Four Prc; no luminous tissue on iris; CO3 with ism; pubic plates of pelvic bones widely ossified, keel; orbital shelf of C04 moderate; no enlarged meeting in midline; 13 to 14 dorsal rays dentigerous area on anterior portion of premaxil- ...... Lampanyctodes lary; anterior tip of urohyal slightly split or with 25B. PO level; PVO vertical; VO level or VO, ele- two distinct heads; ventral series of procurrent vated; no caudal luminous glands, or luminous caudal rays with posterior spines 19 glands small, or supracaudal gland only in males 19A. PO4 elevated; V02 elevated; CO3 lateral shelf as a large, single organ margined with pigment; strongly concave; jaws long, extending one or pubic plate of pelvic bones weakly or moderately more eye diameters behind posterior margin of ossified, not meeting in midline; 15 to 26 dorsal orbit; opercular head of hyomandibula with rays 26 small dorsal process; first pharyngobranchial 26A. VO, elevated; luminous tissue at bases of dorsal with three tooth plates; ten ossified distal pecto- and anal fins and other areas of head and body; ral radials; hypural flange moderate; only ventral secondary photophores restricted to lateral line; series of procurrent caudal rays with posterior one cheek photophore; C05 without keel or spines Lepidophanes ridge; posterodorsal expansion of maxillary long; 198. PO level; VO slightly arched; CO3 lateral shelf supramaxillary a small, rectangular remnant or perpendicular; jaws moderate, extending one- none; dentary with inner row of enlarged teeth; half eye diameter behind posterior margin of posterior portion of dentary with small dorsal orbit; no dorsal process on opercular head of expansion; basibranchial plate extending behind hyomandibula; first pharyngobranchial with one third hypobranchial; 13 to 14 anal rays tooth plate; no ossified distal pectoral radials; ...... Hintonia hypural flange well developed; both dorsal and 26B. VO level; luminous tissue may be present on ventral series of procurrent caudal rays with pos- other parts of body, but never at bases of dorsal terior spines Ceratoscopelus and anal fins; secondary photophores absent, or present over entire head and body; none or three 20A. One Pol; CO3 lateral shelf solid with cup; pos- to seven cheek photophores; C05 with keel or terior portion of dentary without small dorsal ridge; posterodorsal expansion of maxillary expansion; urohyal wing at anterior margin of short; supramaxillary small and L-shaped; den- second hypobranchial ...... Stenobrachius tary teeth small and conical or enlarged teeth 20B. Two Pol; CO3 lateral shelf solid with keel; pos- restricted to posterior portion of dentary; pos- terior portion of dentary with small dorsal ex- terior portion of dentary without dorsal expan- pansion; urohyal wing behind anterior margin of sion; basibranchial plate not extending behind second hypobranchial ...... 21 third hypobranchial; 17 to 22 anal rays 27 54 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13

27A. Secondary photophores on head and body; three teeth, pectoral fins ventral in position, and reduced to seven primary cheek photophores; three Pol, skeletal ossification (Gosline et al., 1966). Two forming a right angle; luminous tissue over orbit characters used by Gosline et al. (1966:16) in the and other areas of body ...... Lampichthys 27B. No secondary photophores; no cheek photo- key to myctophiform families break down in cer- phores; two Pol (rarely three in a horizontal tain myctophid genera. One row of premaxillary line); luminous tissue scattered over body, but teeth is found in the species of Diogenichthys, never over orbit ...... 28 Gonichthys, and Centrobranchus, while Centro- 28A. First A0a not elevated; two (rarely three) Pol in a horizontal line; supra- and infracaudal branchus has the gill rakers reduced to tooth luminous glands present and sexually dimorphic; patches. anterior part of premaxillary with enlarged den- Of the families in the suborder Myctophoidea, tigerous area; posterior part of dentary with the Aulopidae have long been considered the most inner row of enlarged teeth; hypural flange well primitive. A derivation of the Aulopidae from a developed; 37 vertebrae ...... Notoscopelus 28B. First A0a highly elevated; two Pol in line with generalized salmoniform family like the Elopidae last A0a; no caudal luminous glands; anterior has been suggested by Regan (1911) and Gosline part of premaxillary without enlarged dentiger- et al. (1966), primarily on the basis of the presence ous area; all dentary teeth small and conical; of fulcral scales in each family. Greenwood et al. hypural flange moderate; 41 to 45 vertebrae ...... Gymnoscopelus ...... 29 (1966) have recently placed the elopids in another 29A. PV02 opposite pectoral base ...... line of teleost evolution. Weitzman (1967a:532) ...... subgenus Gymnoscopelus has pointed out that other salmoniform families 29B. PV02 dorsal to pectoral base ...... have fulcral scales, and aulopids are not necessarily ...... subgenus Nasolychnus elopoid derivitives. In an unpublished manuscript, Harry (1952) suggested that the myctophoid fami- EVOLUTIONARY RELATIONSHIPS lies have evolved in a number of divergent lines, with an aulopid-like group as the probable ances- Familial Affinities tor. The Synodontidae and Harpadontidae, with the Bathysauridae, are in one line and the Chlo- The order Myctophiformes (Iniomi; Scopeli- rophthalmidae are in another. From the chlo- formes; suborder Myctophoidea, order Salmoni- rophthalmids, the Bathypteroidae and Ipnopidae forms of Greenwood et al., 1966) has been divided arose in one direction (Mead, 1966) and the both formally (Regan, 1911; Berg, 1947) and informally (Marshall, 1955; Gosline et al., 1966) into two suborders, the Myctophoidea and Alepi- sauroidea. The Myctophoidea are comprised of the benthic families Aulopidae, Synodontidae, Harpa- dontidae, Bathysauridae, Chlorophthalmidae, Bathypteroidae, and Ipnopidae and the pelagic or bathypelagic families Neoscopelidae, Myctophidae, and Notosudidae. The latter family has been called the Scopelosauridae by Marshall (1966) and others. However, after 1961 family group names are based on strict priority (Anon., 1961: Art. 40); Notosudidae Parr, 1928, is the proper familial name. The alepisauroid families Paralepididae, Omosudidae, Alepisauridae, Anotopteridae, Ever- mannellidae, and Scopelarchidae are all pelagic or bathypelagic in habitat (Gosline et al., 1966). No consistent characters will distinguish all members of the two suborders from each other, although a number of characters are consistent for most members of either group. The myctophoids usually have more than one row of premaxillary teeth, bladelike gill rakers, pectoral fins placed laterally on the body, and a well-ossified skeleton. The alepisauroids usually have one row of premax- FIGURE 17. Familial relationships within the suborder illary teeth, gill rakers in the form of spines or Myctophoidea. 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 55

Neoscopelidae and Myctophidae in another. The maxillary; nasal dorsal and antorbital ventral to Notosudidae are not placed by Harry, but Marshall nasal organ; no subocular shelf; well-developed (1966) considered this family most closely related distal process on premaxillary; dorsal portion of to the chlorophthalmids. Regan (1911) has pointed extrascapular anterior to posttemporal; posttermi- out the similarities between the chlorophthalmids nal centrum and terminal vertebra incompletely and myctophids and Fraser-Brunner (1949) fused in adults. However, a premaxillary-palatine considered the neoscopelids as ancestral to the ligament is lacking in the Chlorophthalmidae ex- myctophids. The family Myctophidae, according amined. In contrast to both myctophids and neo- to these views, is derived from an aulopid- scopelids the chlorophthalmids have a moderately chlorophthalmid-neoscopelid line of evolution. The to greatly elongated snout; the first circumorbital study of Gosline et al. (1966) supports the sug- rather than the third is the most extensive; the gested familial relationships that are summarized palatine lacks a dorsal wing, but has an extensive in the evolutionary diagram (Fig. 17). anterolateral process which articulates with the The following osteological characters will distin- maxillary; of the posterior four branchiostegal rays guish the neoscopelids from the myctophids: which articulate on the lateral face of the hyoid arch, three or four articulate on the epihyal (in myctophids and neoscopelids only the last two Myctophidae Neoscopelidae articulate on the epihyal); and the basihyal is very nasal anterodorsal to dorsal to nasal large and well ossified. The above diagnosis is nasal organ organ based only on the generalized chlorophthalmid antorbital posterior to ventral to nasal genera Chlorophthalmus and Parasudis, that also nasal organ organ have a very large eye and short jaws ending before subocular shelf present absent the middle of the orbit. The abyssal Bathysaurop- premaxillary- absent present sis, which I have not seen, has a smaller eye and palatine jaws extending behind the orbit, and is intermedi- ligament ate between the generalized chlorophthalmids and distal process of moderate or well developed the bathypteroids and ipnopids, according to Mead premaxillary absent (1966). supramaxillary absent or pres- present as a Although Scopelosaurus of the family Notosudi- ent as a small, long, slender dae is also bathypelagic, it differs in a number of L-shaped element characters from the neoscopelids and myctophids. element Scopelosaurus shares with the Chlorophthalmidae basihyal ossifi- absent or very moderate or an elongated snout, the absence of a dorsal wing cation small large on the palatine, the absence of a premaxillary- dorsal extra- anterolateral to anterior to post- palatine ligament, the enlarged first circumorbital, scapular posttemporal temporal and the articulation of the last three or four bran- terminal verte- fused in adults incompletely chiostegal rays on the epihyal. This last character bra and fused in postterminal adults. relates chlorophthalmids and notosudids to the centrum bathypteroids and ipnopids, and the families of the suborder Alepisauroidea. The Aulopidae, Synodontidae, and Harpadontidae have a branchi- Contrary to the statement of Rosen and Patter- ostegal ray pattern unlike either the chlorophthal- son (1969:448), the epurals of myctophids are mids or myctophids (McAllister, 1968). Characters similar to those of neoscopelids and most other separating Scopelosaurus from the chlorophthal- families in the suborder. Of the three neoscopelid mids are listed by Marshall (1966:197), to which genera, Scopelengys, with a poorly ossified skele- may be added for Scopelosaurus a poorly ossified ton, small eyes, no mesopterygoid teeth, and small skeleton, a relatively small eye, the lack of a distal pharyngobranchial tooth plates is most distinct process on the premaxillary and the presence of a from the myctophids. No osteological characters very long anterior rod on the urohyal. The charac- examined clearly indicate whether Neoscopelus or ters shared by notosudids and neoscopelids, to the Solivomer is more closely related to the lantern- exclusion of the myctophids, are all shared by the fishes, although the presence of photophores in chlorophthalmids and neoscopelids, namely: a Neoscopelus is suggestive. long, slender supramaxillary; nasal anterodorsal The chlorophthalmids share the following char- and antorbital ventral to nasal organ; circumor- acters with the neoscopelids: long, slender supra- bitals without subocular shelf; ossified basihyal; 56 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 and postterminal centrum and terminal vertebra strongly suggest that the similarities in photophore incompletely fused. patterns between gonostomatids and myctophids The osteological similarities and differences out- are the result of convergence, and the simplest lined above for the various myctophiform families explanation of myctophid ancestry is with the of the suborder Myctophoidea support the hypo- aulopid-chlorophthalmid-neoscopelid line. thesis that the line of evolution approximates the present Aulopidae-Chlorophthalmidae-Neoscope- Subfamilial Relationships lidae-Myctophidae one, with the Notosudidae an Within the family Myctophidae, a number of offshoot derived from the Chlorophthalmidae. The evolutionary lines are apparent; the lines fall into similarities between Scopelosaurus and the alepi- two major groups here recognized as subfamilies, sauroid families suggest that the Notosudidae may the Myctophinae and Lampanyctinae. While it is be close to the ancestral stock of that suborder. difficult to discuss the two groups in terms of primi- However, the evidence does not clearly indicate tive and advanced states of evolution, due to the which direction evolution has proceeded within the specializations found in members of each group, a myctophoid families. While Fraser-Brunner (1949) distinct trend in some characters is noticeable considered the neoscopelids ancestral to the mycto- within the family as a whole. Short jaws, unsculp- phids, he suggested a derivation of these groups tured circumorbitals with an extensive orbital shelf, from a salmoniform stock similar to the Gonosto- two extrascapulars, the absence of a posteromedial matidae. His hypothesis is based solely upon the shelf on the cleithrum, a ventral position for most striking similarities of photophore patterns in Neo- photophores, including the Prc series with only scopelus, the myctophid genera Protomyctophum two photophores, the lack of secondary photo- and Electrona, and primitive gonostomatids like phores and cheek photophores, the restriction of Vinciguerria. Fraser-Brunner's hypothesis requires luminous tissue to the caudal glands, and the sexual that the neoscopelids are the primitive myctophi- dimorphism of those glands are found in some or form family, with a derivation of the myctophids all members of the Myctophinae and none or few in one line and the chlorophthalmids in another, of the Lampanyctinae. At the other end of the and a subsequent radiation from the Chlorophthal- spectrum, within the Lampanyctinae, are found midae. A number of problems are raised by such a long jaws, sculptured circumorbitals with a mod- phylogeny. The relative primitiveness of the Aulop- erate orbital shelf, one extrascapular, a postero- idae, and the derivation of the Synodontidae and medial cleithral shelf, a number of photophores Harpadontidae from this family could only be ex- near or above the lateral line, including the last of plained as an independent evolution of this line the Prc series that usually numbers from three to from some premyctophiform stock. In this instance nine, the presence of secondary photophores and the myctophiforms would have to be regarded as luminous tissue over the body, the presence of a polyphyletic assemblage and the characters the cheek photophores, and the usual lack of sexual families have in common, loss of mesocoracoid dimorphism in the caudal luminous glands. The arch, exclusion of the maxillary from the gape, etc., problem is to determine in which direction evolu- would entail evolutionary convergence. Such a tion has occurred; that is, is the Protomyctophum- convergence is considered unlikely, for it would Electrona stock closer to the ancestral myctophid or involve parallel evolutionary changes in a number is some form like Lam panyctus, Scopelopsis, or of functionally unrelated units of the skeleton. The Diaphus the more primitive, generalized lanternfish. neoscopelids possess advanced characters which The problem is complex, for the primitive group mitigate against their position as the basal myc- has doubtless become considerably specialized tophiform family. The presence of an enlarged since the origin of the family. distal process on the premaxillary, a premaxillary- As noted above, the myctophids are most similar palatine ligament, and the articulation of only two to, and presumably most closely related to the branchiostegal rays on the epihyal are all advanced Neoscopelidae. Parr (1928:48) suggested that characters, that have suggested to Greenwood et al. Scopelopsis, with a photophore under each scale, (1966) that the neoscopelids, or neoscopelid-like may be most closely related to Neoscopelus, which fishes, may be ancestral to a major line of percoid has a photophore under each scale on the ventral radiation. Recently Moser and Ahlstrom (1970: portion of the body. Fraser-Brunner (1949) placed 141-2) have stated that the larvae of Chlorophthal- Scopelopsis near Hintonia, a member of the Lam- mus, Scopelengys, and myctophids are similar and panyctinae; he considered the Protomyctophum- show striking differences from the larvae of Electrona stock closest to the neoscopelids, on the gonostomatids. The arguments advanced above basis of an expanded posterior maxillary and ven- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 57

tral photophores. The osteological evidence sup- myctophines, and no lampanyctines, are evidence ports the placement of Scopelopsis near Hintonia. of the close relationship between the neoscopelids A comparison of the neoscopelid genera Neo- and the subfamily Myctophinae. scopelus and Solivomer reveals differences in The osteological evidence suggests that Neo- osteology which parallel the trends found in the scopelus and Protomyctophum or Electrona are Myctophidae. Neoscopelus, with a large, eye, has closely related. In addition Fraser-Brunner (1949) many characters in common with Protomyctophum has developed a hypothesis on the phylogeny of and Electrona. The jaws are short, ending under lanternfishes that is based upon the position of the the posterior margin of the orbit; the maxillary photophores. He considered the primitive condition ridge is absent; the distal premaxillary process is to be two ventral rows of body photophores, a extensive (moderate in Protomyctophum); the condition essentially retained in Protomyctophum posterior portion of the maxillary is widely ex- and Electrona. During the course of evolution, panded; the circumorbitals lack sculpturing; the various photophores migrated dorsally on the body, symplectic extends above the dorsal margin of the as found in most Lampanyctinae. The most con- quadrate; there is no lateral strut on the metapter- vincing evidence in support of his scheme is the ygoid (small in Protomyctophum); the orbital relation of photophores to scales. Most body pho- process of the hyomandibula is slight (absent in tophores, and particularly those in the ventral-most Protomyctophum); and there is only a slight pos- row, are associated with the meristic series of teromedial shelf on the cleithrum (the coracoid scales. However, those photophores which have articulates on the main shaft of the cleithrum, as migrated dorsally are associated with small scales in Protomyctophum). Neoscopelus shares with that break up the general meristic arrangement of some or all members of the Lampanyctinae the scales. following characters: a supramaxillary, one extra- However, on the basis of larval evidence, Moser scapular, and a pronounced ethmoid process of and Ahlstrom (1970: 141-2) have argued that the the first circumorbital. In Solivomer the eye is two subfamilies diverged early in the evolutionary smaller and the jaws extend behind the posterior history of the family and neither can be considered margin of the orbit about one orbital diameter; the more primitive. Their argument is based upon the distal premaxillary process is large, but less the similarities between the larvae of Scopelengys, pronounced than in Neoscopelus; the symplectic the Chlorophthalmidae, and those of the Lam- does not extend above the quadrate; a small lateral panyctinae. They considered that evolution had strut extends just dorsal to the main body of the proceeded at different stages in the life histories of metapterygoid; and the orbital process of the hyo- each subfamily; the Myctophinae have retained mandibula is extensive. Except for the complete relatively primitive adult morphology and special- lack of photophores in Solivomer, Neoscopelus izations have radiated in larval stages, while the and Solivomer are similar in most other characters Lampanyctinae have remained more primitive as examined. larvae but have undergone considerable special- The osteological characters shared by Solivomer izations as adults. and the lampanyctines are mostly the result of a Moser and Ahlstrom's (1970) view of the evo- parallel change in one anatomical feature, the lutionary history of the subfamilies creates a few lengthening of the jaws relative to the size of the problems in interpreting the apparent trends in orbit. In long-jawed forms, the entire suspensory adult morphology. The similarities between Pro- apparatus must curve posteriorly from the pterotic tomyctophum and Neoscopelus are explicable by to the articular of the lower jaw. The increased the hypothesis of Moser and Ahlstrom. However, curvature of the hyomandibula and posterior dis- two trends among the Myctophinae, the elongation placement of the quadrate, symplectic, and metap- of the jaws culminating in the moderate jaws of the terygoid are doubtless correlated with the increase Gonichthyini, and the elevation of photophores on in the orbital process of the hyomandibula, the the side of the body found in a number of species shortening of the symplectic in relation to the in the subfamily clearly foreshadow similar ad- quadrate, and the extension of the lateral strut of vances in the Lampanyctinae. Without the larval the metapterygoid. The expanded posterior end of evidence, the simplest explanation would have been the maxillary, extensive distal process on the pre- that Lampanyctinae evolved from the Myctophinae maxillary, lack of a maxillary ridge, and lack of after the latter had reached an evolutionary stage a shelf on the cleithrum with which the ventral near the present form of perhaps Myctophum or portion of the coracoid articulates, characters Hygophum. However, the larval evidence indicates shared by all of the neoscopelids, a number of that the adult specializations of lengthened jaws 58 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 and elevated photophores occurred independently lampanyctine and its relationships are discussed in in the two subfamilies. detail below. Each specialization probably has considerable The presence of two extrascapulars in the primi- selective pressure acting in its favor. Lengthened tive adult condition and fusion of these bones into jaws doubtless increase feeding efficiency and an one element in the advanced agrees well with Wil- increase in jaw length has apparently occurred liston's Rule (see Simpson, 1949: 253), that a loss independently a number of times in the suborder or fusion of elements is more common in advanced Myctophoidea. In Aulopus, Chlorophthalmus, and than in primitive form. The presence of a single, Neoscopelus the jaws are short and lengthening large extrascapular in the family Neoscopelidae has occurred in the Synodontidae and Harpo- does not negate the hypothesis that the Mycto- dontidae from Aulopus, in the chlorophthalmid phinae display the most primitive adult condition Bathysauropsis and the Bathyopteroidae from in lanternfishes. The position of the dorsal portion Chlorophthalmus, and in Solivomer, Scopelengys, of the extrascapular is anterior to the dorsal fork and the Lampanyctinae from Neoscopelus. In addi- of the posttemporal in neoscopelids, rather than tion, the presence of short jaws in some members of anterolateral to the posttemporal as in myctophids. the Lampanyctinae, such as a few species of Dia- This suggests that the extrascapular fusion may phus and Bolinichthys, may represent the primitive have been an independent event in neoscopelids, condition rather than a secondary shortening. Al- after the evolutionary divergence of the Mycto- though the lengthening of jaws involves a complex phidae. series of changes in a number of skeletal elements, Tribal Relationships the character is nonetheless apparently a plastic Six major evolutionary lines are apparent in the one, and its independent development in the Myc- family, two in the subfamily Myctophinae and tophinae is not difficult to accept. four in the subfamily Lampanyctinae (Fig. 18), If the primary function of body photophores in that are recognized as tribes. The Myctophini, with modern myctophids is species recognition, as will seven genera, is the largest tribe in the subfamily be argued in the final section, the elevation of Myctophinae. The tribe Gonichthyini is a special- photophores to the sides of the body probably en- ized group of four genera commonly termed slen- hances such recognition. If so, selection would dertailed lanternfishes (Becker, 1964) in refer- strongly favor such photophore migration and ence to the very slender caudal peduncle. Within could explain the independent evolution found in the Lampanyctinae, the monotypic tribe Notol- both subfamilies. In summary, an early split of the ychnini is represented by Notolychnus valdiviae. subfamilies with a caenogenetic condition prevail- This species has characters of both subfamilies, ing in the Myctophinae and the Lampanyctinae although the total complex of characters suggests being palingenetic (Moser and Ahlstrom, 1970: the closest affinities are with the lampanyctines. 142) is the simplest explanation to account for The other tribes in the subfamily are the Lam- both adult and larval morphology. panyctini with eight genera, the Diaphini with Few characters will unequivocally separate all two genera, and the Gymnoscopelini with six members of the two subfamilies. In the Mycto- genera. phinae, both dorsal and ventral extrascapulars are Three evolutionary groups are apparent within present, or the dorsal element has been lost. The the tribe Myctophini. The first is represented by two elements have fused in the Lampanyctinae, the primitive genera Protomyctophum and Elec- although in Notolychnus the extrascapular ele- trona, the second by Diogenichthys and Bentho- ments are unossified and the condition is uncertain. sema, and the third by Hygophum, Myctophum, In all myctophines the cleithrum lacks a postero- and Symbolophorus. Wisner (1963b) erected the medial shelf, which is present in all lampanyctines tribe Electronini to include the genera Protom- except Notolychnus. One or two Prc photophores yctophum, Hierops (here considered a subgenus are present in the Myctophinae and Notolychnus, of Protomyctophum), Electrona, and Metelectrona while three to nine Prcs occur in all other Lam- (here considered a synonym of Electrona). The panyctinae except Scopelopsis, with indistinct pri- distinguishing characters of the tribe were listed mary photophores. The eyes of larval myctophines as ". . the PLO and PVO photophores located are elliptical in outline, while those of larval lam- below, or but very little above the lower edge of panyctines are round. Notolychnus is intermediate, the pectoral base, large eyes, and by relatively having larvae with semi-elliptical eyes (Moser, and blunt, non-projecting snouts, and entirely terminal Ahlstrom, 1970). The position of Notolychnus is mouths." The large eye, blunt snout, and terminal obviously a problem; I regard it as a primitive mouth will differentiate the above genera from the 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 59

Gonichthyini and some forms of Myctophum, but to members of these genera. In addition, M. auro- these characters are also found in a number of laternatum has a moderately slender caudal pe- other forms in the Myctophini: Benthosema, Hy- duncle, as do the Gonichthyini, while M. asperum gophum, Symbolophorus, and most Myctophum. has the teeth of the third pharyngobranchial plate The PVO photophores are below or but slightly modified as pegs, like those found in Gonichthys. above the ventral margin of the pectoral base in Many species of Myctophum and Symbolophorus all forms of the Myctophini and even in the have well-ossified skeletons; the Gonichthyini and Gonichthyini. Thus the only distinguishing char- the above two genera include the most heavily ossi- acteristic of the tribe is the location of the PLO fied forms within the family, and also include photophore below or near the ventral margin of the species which have some of the shallowest vertical pectoral base; the PLO is distinctly above the pec- distribution of all myctophids. The relatively low toral base in all other forms of the Myctophini. An position of the PLO photophore has prompted analysis of the osteological variation reveals that Bolin (1939: 100-101) to suggest that the relation- there are no osteological characters which will dis- ship of this group is with the Protomyctophum- tinguish Protomyctophum and Electrona from all Electrona stock; Fraser-Brunner (1949:1060) also other members of the Myctophini, and the two considered this a possibility. However, the complex genera here are considered primitive representa- of characters described above are a strong indica- tives of the tribe Myctophini. tion that a group at least as advanced as Mycto- The tribe Gonichthyini comprises four genera phum was the ancestor of the tribe. strikingly similar in body form, with a projecting Two evolutionary lines are apparent within the snout, subterminal mouth, slender caudal peduncle, Gonichthyini; Gonichthys and Centrobranchus are and a relatively well-ossified skeleton. The project- closely related and Loweina and Tarletonbeania ing snout, moderate jaw length, reduced antorbital, are also apparently a generic pair. The relation- weak fusion of the tips of the procurrent caudal ships of these genera willl be discussed in detail rays, and the PLO photophore opposite or very in a later section. The distinctiveness of the generic slightly above the pectoral base will distinguish all pairs is apparent in the larval morphology as well members of this tribe from the closely related as the adult. Moser and Ahlstrom (1970: 138-140) Myctophini. A number of characters suggest that have indicated that the larval characteristics of the Myctophum-Symbolophorus line gave rise to Loweina and Tarletonbeania are so distinct from the slendertails. A free preopercular flag and an those of Gonichthys and Centrobranchus that the extensively developed hypural flange are limited generic pairs have different ancestors and cannot be included in the same tribe. Their argument is

,SOS based primarily on the structure of the larval eyes; 0S ‘'S Loweina 00 ‘ "SEE ` and Tarletonbeania have relatively unspe- 00' ,0 OSR cialized eyes similar to those of Protomyctophum and Electrona, while Gonichthys and Centrobran- chus possess larval eyes with extensive ventral choroid tissue, a condition considered an extension of a trend in specialization apparent in Hygophum, Myctophum, and Symbolophorus. Other larval features of Loweina and Tarletonbeania, such as head, body, and gut shape, and extensive median fin folds, are considered specialized. Moser and Ahlstrom concluded that the similarities of adult morphology in the two generic pairs are the result of evolutionary convergence. The differences between larval and adult mor- phology are difficult to reconcile in these four genera. If convergence of adult features were re- sponsible for the similarities, this convergence must have occurred in a number of functionallly unre- lated systems. The projecting snout, expanded nasal, and reduced antorbital are probably interre- FIGURE 18. Tribal relationships within the family lated changes reflecting one evolutionary advance; Myctophidae. the slender caudal peduncle and distinctive caudal 60 BULLETIN OF THE NATURAL HISTOR Y MUSEUM OF LOS ANGELES COUNTY No. 13 skeleton development are also probably correlated currents and/ or a more active pursuit of food with each other (Moser and Ahlstrom, 1970: 140), organisms are causative factors. Although lantern- as are the fused hypurals. However, in addition fishes as a group are strikingly similar in their to the similarities in these two functional mor- overall body plan and, apparently, in the major phological units, the four genera also share the features of their ecology, such as vertical migration, following characters which are not found in any subtle specializations in morphology and ecology other members of the subfamily: a moderately have certainly occurred. Distressingly little is lengthened jaw and the elevation of the PLO photo- known of the ecology of all but a few species; phore opposite the pectoral fin base. These four however, it appears that the streamlined Gonichth- are also among the most heavily ossified of the yini represent the end result of one line of special- family. Finally, the otoliths of representatives of ization within the Myctophidae. the four genera are more similar to each other than As indicated above, the monotypic tribe Noto- to any other member of the subfamily (John Fitch, lychnini is difficult to place in either subfamily. personal communication), suggesting a common Bolin (1946) considered the species a derivative ancestry. That convergence is responsible for all of Triphoturus, a close relative of Lampanyctus. of the features described seems remarkably coin- Fraser-Brunner (1949) discussed this possibility cidental. and thought that the origin of Notolychnus was As an alternative to the evolutionary history pro- from the same general stock as Lam padena and posed for the four genera by Moser and Ahlstrom, Lam panyctus , while he pointed out the characters the complex of characters suggest a common an- shared with more primitive myctophids. Three cestor arising from the Hygophum-Myctophum- osteological characters of Notolychnus are found Symbolophorus complex. The larval specializations in many forms of the Lampanyctinae and in no of Loweina and Tarletonbeania would have devel- Myctophinae: long jaw; small dorsal process on oped after the split of Gonichthys and Centro- posterior part of dentary; and hyomandibular nerve branchus. Thus the only problem encountered in foramen between anterior and median hyoman- this evolutionary scheme is the unspecialized con- dibular heads. In addition, the position of four dition of the larval eyes of Loweina and Tarleton- photophores high above the lateral line is a condi- beania when compared with those of Hygophum, tion most closely approached by Triphoturus, with Myctophum, Symbolophorus, Gonichthys, and five photophores on the lateral line. Another char- Centrobranchus. While the reversibility of a spe- acter shared with Triphoturus is the weak ossifi- cialized structure is an evolutionary event rarely cation of much of the skeleton, notably the cir- documented (Rensch, 1959: 124), it appears a cumorbital bones. The presence of a foramen in more plausible explanation than the independent the ceratohyal, found only in Notolychnus and convergence of five unrelated morphological fea- Triphoturus, may be correlated with the weak tures. Although future studies may yield data to ossification. Some characters, however, suggest a resolve the apparent conflict, in this study the four relationship of Notolychnus with the subfamily genera are placed in one tribe, reflecting an as- Myctophinae. The lack of a posteromedial shelf on sumed common ancestry. the cleithrum and the presence of only two Prc Many of the specializations of the Gonichthyini photophores are conditions found in all Mycto- are probably related to their nocturnal visits to the phinae and no other Lampanyctinae. The fusion ocean surface. Tarletonbeania occurs in the sur- of hypurals into a dorsal and ventral plate and the face waters off Oregon (Pearcy, 1964), and I have reduction of pelvic rays are conditions duplicated dipnetted species of the other three genera in the in some species of the Gonichthyini. The metap- Atlantic. The projecting snout, slender caudal pe- terygoid strut extends dorsally above the main duncle, and strong ossification are probably adap- body of the metapterygoid; this is also true in most tations to rapid swimming. Hartmann and Weikert Lampanytinae and in none of the Myctophinae (1970) have suggested the projecting snout and except Centrobranchus. Undivided caudal lumin- well-developed nasal organs of Centrobranchus are ous glands margined with heavy black pigment are important in obtaining pelagic molluscs. However, also found in Lam padena, Taaningichthys, and in attempting to determine the modifications neces- Notoscopelus of the Lampanyctinae and Protom- sary for this specialized feeding, they did not con- yctophum (Hierops), Diogenichthys, Benthosema, sider the modified crushing pharyngeal teeth in and Hygophum of the Myctophinae. Finally, the this genus. Shallow water forms are often stronger condition of the eyes in Notolychnus larvae is in- swimmers than species which live at considerable termediate between the elliptical state in the Myc- depths (Marshall, 1960). Perhaps stronger surface tophinae and the round state in the Lampanyctinae 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 61 (Moser and Ahlstrom, 1970). I interpret the above Lampanyctini from the Diaphini, while the lack characters to indicate that Notolychnus diverged of a supramaxillary, a ridge or keel on the fifth from the ancestral stock of the subfamily Lam- circumorbital, a Dn, and the presence of a mod- panyctinae, and although it has retained a number erate or long ischial ligament directed posteriorly of characters in common with the subfamily Myc- will separate the group from the Gymnoscopelini. tophinae, it belongs in the former group. The It may be argued that Lam padena and Taaning- erection of a monotypic tribe is admittedly beg- ichthys deserve a tribe of their own. While they ging the question of relationship; however, I think are not as closely related to the other five genera that the unique specializations of Notolychnus, as they are to each other, their relationship is namely the very weak ossification, reduction of clearly with the Lampanyctini, as evidenced by palatal elements, and modified photophore pattern, the characters shared with Bolinichthys. The ori- and its intermediate position between the two sub- gins of the Lampanyctini are near the ancestral families, warrant this decision. If Notolychnus stock of the subfamily Lampanyctinae. The line were to be included in another tribe, the Lampan- apparently diverged before the split of the Diaphini yctini would seem the proper allocation. The re- and Gymnoscopelini. tention of primitive adult characters in Notol- Modifications of the Lampanyctini are many. ychnus is probably the result of its ancestry within The caudal luminous glands of Lam padena and the Myctophinae and early divergence from the Taaningichthys show the extreme development of other Lampanyctinae; these same characters miti- a single, unsegmented gland margined with black gate against derivation of Notolychnus from Tri- pigment. Secondary photophores and luminous photurus. tisssue are present in some species of the tribe. The most striking specializations of Notolychnus The orbital organ in all species is restricted to a are the weak ossification of the skeleton and the small, single Vn. All species have a single row of small size of mature individuals; no specimens over moderately or strongly hooked teeth on the pos- 25 mm standard length are known. Not enough terior portion of the dentary. These specialized information is available on larval and juvenile teeth, which are found in different areas of the skeletal features to determine if the lack of ossifi- premaxillary and dentary in various other lantern- cation is the result of attaing sexual maturity at a fish genera, are doubtless a modification for feed- very small size; weak ossification among larval ing. The anteriorly directed teeth in the posterior myctophids is common. However, some forms of portion of the jaws probably inhibit the loss of Lampanyctus and Triphoturus reach larger adult food items which are in the mouth cavity. size (50 to 100 mm) and are poorly ossified. On As presently understood, the tribe Diaphini is the other hand, species of the genus Diogenichthys represented by only two genera, Lobianchia and mature at less than 25 mm and are relatively well Diaphus. Diaphus has more than 100 nominal ossified. It would appear that the weak ossification species and probably about 50 of these are valid in Notolychnus is' not entirely the result of accel- (Nafpaktitis, personal communication). A future erated development of the sexual organs (or arrest division of this large assemblage into a number of of somatic development, as the case may be) but genera is likely, although detailed information is a result of environmental selection. The functional not available on enough of the species to facilitate significance of the specializations of Notolychnus such a division at the present time. Because of the remains conjectural. wide range of morphological types present in the The tribe Lampanyctini consists of eight genera genus Diaphus, few characters will distinguish all within three definite lines. Lam padena and Taan- members of the tribe from all other species in the ingichthys are closely related, as are Bolinichthys, subfamily Lampanyctinae. Only the presence of Lepidophanes, and Ceratoscopelus; Stenobrachius, from one to seven ossified distal pectoral radials is Lampanyctus, and Triphoturus represent the third diagnostic for the tribe. The Diaphini can be dis- line. No single character will differentiate all mem- tinguished from the Gymnoscopelini by the ab- bers of the tribe from all other species within the sence of a supramaxillary, the presence of five to subfamily. Taken individuallly, the specializations seven ventral procurrent rays, the elevated PO. of the Notolychnini have been noted above. The and the inclined PVO, while the widely ossified lack of a widely ossified pubic plate in the pelvic pubic plate of the pelvic girdle, lack of moderately girdle, the presence of moderately or strongly re- or strongly hooked teeth on the posterior portion curved teeth on the posterior portion of the den- of the dentary, and the presence of a Dn will dis- tary, the lack of any ossified distal pectoral radials, tinguish the group from the Lampanyctini. The and the lack of a Dn will distinguish the tribe Diaphini and Gymnoscopelini are closely related, 62 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 for the most primitive genus of each group, Lo- although the detailed ecology of any species of bianchia of the Diaphini and Lampanyctodes of the the group is virtually unknown. The presence of a Gymnoscopelini, share a number of characters. supramaxillary in such an advanced group, and Each form has widely ossified pubic plates, a rela- its absence in all other lanternfishes, is difficult to tively low number of ventral procurrent rays, well- explain. It could be argued that a supramaxillary developed caudal glands, one or two elevated PO was present in ancestral myctophids (a supramax- photophores, and an arched or elevated series of illary is present in the closely related Neoscope- VO photophores; none of these characters are lidae) and all other lines of myctophids have lost found in the other gymnoscopeline genera. The this element. However, such a loss must have oc- fifth circumorbital has a curved outline and bears curred independently in four lines: within the a small keel or ridge in most Diaphini and Gym- subfamily Myctophinae after the divergence of noscopelini. the Lampanyctinae, independently in the ancestral The most noteworthy feature of the genus Dia- stocks of the tribes Diaphini and Lampanyctini, phus is the lack of caudal glands and the extensive and within the Gymnoscopelini itself in Hintonia. development of luminous tissue around the anterior In addition, the supramaxillary of this group is portion of the orbit, the Dn and Vn organs. These morphologically unlike that of the neoscopelids. luminous bodies have apparently taken over both The gymnoscopeline supramaxillary is very small, the sexual recognition function of the caudal L-shaped, and at the posterior tip of the maxillary, glands and the specific recognition function of the with the short leg of the bone lying medial to the body photophores. In this speciose group there are maxillary; in neoscopelids the element is long, thin, no caudal glands and the body photophores show and lies above and parallel to the posterior portion little variation, while the antorbital light organs of the maxillary. Another possible explanation is are often sexually dimorphic and species specific that the supramaxillary has arisen de novo in the in shape and development. At present, there is no ancestral stock of the Gymnoscopelini, after diver- explanation to account for the successful radiation gence from the Diaphini. The functional signifi- of the tribe Diaphini. cance of the element is not clear. The increase in The tribe Gymnoscopelini is a specialized group the number of procurrent caudal rays, both dorsal of six genera, most of which are restricted to the0 and ventral, in most of the Gymnoscopelini may be oceans of the southern hemisphere below 30 related to increased tail musculature for stronger South; only species of the genus Notoscopelus are propulsion. The presence of both a supramaxillary found in all major oceans. The invariable presence and an increased number of procurrent rays could of a small supramaxillary will distinguish all mem- be considered indicative of a primitive group, if bers of the Gymnoscopelini except Hintonia from Williston's Rule were applied. However, other all other lanternfishes, while the high number of osteological features, such as long jaws, sculptured ventral procurrent rays, 13 in Hintonia, will dis- circumorbitals, and a posteromedial shelf on the tinguish this genus and most of the other members cleithrum, and the specializations of luminous of the tribe from all other myctophid species. Char- tissue, all indicate that the tribe represents an acters differentiating the Gymnoscopelini from the advanced group of lanternfishes. The modifications Diaphini have been described above. The presence of photophore patterns and other luminous organs of a short, medially directed ischial ligament is the within the group are considerable. Caudal glands only character which will distinguish all gymno- are well developed or absent, secondary photo- scopelines from the tribe Lampanyctini, which phores are extensive or absent, and the orbital have a moderate to long, posteromedially directed organs may be very well developed. An indication ligament; all forms of the Gymnoscopelini except of the diversity in form is the fact that four of the Hintonia have a small keel or ridge on the fifth six genera, Lampanyctodes, Lam pichthys, Hin- circumorbital which the Lampanyctini lack. As tonia, and Scopelopsis, are monotypic. noted above, the Gymnoscopelini and Diaphini In the introduction, it was stated that one as- have apparently diverged from a common stock; sumption of this study was that the family is mono- the genus Lam panyctodes is the most primitive phyletic in origin. The previous descriptions of gymnoscopeline, with a number of characters in tribes support the validity of this assumption. common with the Diaphini. If this essentially inter- While the major differences within the family are mediate form lacked a supramaxillary, its place- found between the two subfamilies, a number of ment into one of the two tribes would be difficult. evolutionary trends which transcend the subfamilial Structurally, members of the Gymnoscopelini division are evident. There is no indication that are among the most specialized of lanternfishes, the family arose more than one ancestor. 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 63

Generic Relationships Of the five species of the subgenus Protomyc- Myctophini. Although closely related, the seven tophum, P. anderssoni is somewhat isolated in genera of the tribe Myctophini form a number of morphology. This species is a relatively slender generic groups. Due to the many similarities with fish with a series of individual supracaudal glands Neoscopelus, Protomyctophum is considered to in the male and the SAO usually reduced to two approach the most primitive adult condition in the in number and placed very low on the body, almost tribe and family. The absence of a maxillary shelf in a line with the VO and AO series. P. normani, distinguishes the genus from all others in the tribe, P. holini, and P. andriashevi are deeper bodied while the origin of the urohyal wing behind the forms, approaching the condition found in Hierops, origin of the second hypobranchials and the hori- with a single supracaudal gland, either very small zontal position of the two PVO photophores will or long and narrow, and three or four SAO photo- distinguish Protomyctophum from the closely re- phores that are distinctly dorsal to the ventral series lated Electrona. Two species groups, here con- of photophores. P. ten isoni is intermediate between sidered subgenera, are recognizable within the the two types, with a moderately deep body, a genus Protomyctophum. Members of the nominal series of individual supracaudal glands, and three subgenus have a broad interorbital area, with wide lateral SAO photophores. The deep-bodied species frontals between the orbits. In the subgenus Hier- group probably gave rise to the Hierops group, ops, the frontals are moderately or considerably that are very deep-bodied, and also may be similar narrowed between the orbits, and the lens and to the ancestral stock of Electrona; no slender- pupil of the eye are displaced dorsally to create bodied species are known for this latter genus. The a semitelescopic eye. Such a major evolutionary five species of Protomyctophum are all Antarctic change could be considered of generic significance, or subantarctic in distribution, while two of the and Hierops has been given generic status by Bolin species of Hierops are subantarctic and three spe- (1959) and Wisner (1963b). However, as An- cies are found in the northern hemisphere. driashev (1962) pointed out, Protomyctophum No single character will differentiate Electrona (Hierops) thompsoni is intermediate in this im- from all other genera in the tribe Myctophini. The portant character. The eye does not appear dorsally low position of the PLO will distinguish Electrona displaced and the reduction of the frontals between from all genera except Protomyctophum and the the orbits is only about half that found in the other inclined position of the PVO photophores and the four species of the subgenus. The other distinguish- presence of a maxillary shelf are characters of ing feature of Hierops is the presence of a single, Electrona not found in Protomyctophum. Except supracaudal luminous gland margined with black for the low position of the PLO, no other feature pigment in males. Although a variety of supra- is shared by all species of Electrona and Protomyc- caudal gland types is found in the five species of tophum exclusively. However, a premaxillary shelf the subgenus Protomyctophum, none is of the type and an unbroken series of AO photophores occur found in Hierops. The presence of a single supra- in all species of Protomyctophum and some of caudal gland in P. thompsoni reflects its relation- Electrona. These three characters indicate that ship to the other species of Hierops, and the mod- Electrona and Protomyctophum are closely related. erately narrowed frontals suggest it is the most The occurrence of a premaxillary shelf, considered primitive species of this apparently monophyletic homologous to the distal premaxillary process of subgenus. I do not think that generic recognition neoscopelids, an unbroken series of AO photo- is warranted when a species is intermediate in the phores, and the horizontal position of the PLO and major adaptive shift of the group. In addition, the PVO photophores indicate that Protomyctophum larvae of the species of Hierops do not differ sig- is the more primitive group. Since the orbital and nificantly from those of Protomyctophum (Pertseva- supracaudal gland specializations of the subgenus Ostroumova, 1967; Moser and Ahlstrom, 1970), Hierops are not present in any Electrona, the sub- while the larvae of most myctophid genera are genus Protomyctophum is probably the most simi- distinctive (Moser and Ahlstrom, 1970). Although lar to any ancestor of Electrona. the species of Hierops apparently form a monophy- Wisner (1963b) described the genus Metelec- letic assemblage, generic status would indicate trona for a single new species of Electrona-like fish. that this group is as distinct morphologically and No definitive diagnosis of the genus was presented, evolutionarily from Protomyctophum as are the although it was pointed out that in Metelectrona species of Electrona, which apparently diverged the palatine teeth are modified as three strong from the subgenus Protomyctophum in another fangs, the VO, is elevated, and the AO series is line; such is not the case. broken by two elevated Pol photophores. Ap- 64 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13 parently Wisner considered the broken AO series of Diogenichthys, no osteological character will to be the most significant generic character, for it differentiate any one genus from all of the others. is the only one used to differentiate the new species Osteological characters have a mosaic pattern of in his key to the genera Protomyctophum, Hierops, distribution within the genera and it is difficult to Electrona, and Metelectrona. However, Bussing interpret evolutionary lines and relationships on the (1965) has pointed out the great variability in the bases of these characters. For instance, the pos- position of AO and Pol photophores in Metelec- terior plate of the third circumorbital is incom- trona. The slightly raised position of one AO pho- pletely fused to the lateral shelf in Hygophum and tophore (Bussing, 1965: Fig. 6B) is also found in some forms of Myctophum and Symbolophorus; some specimens of Electrona paucirastra and E. a free preopercular flag is present only in some subasper. The enlarged palatine teeth of Metelec- Myctophum and some Symbolophorus; a dentate trona are also found in E. antarctica (see Fig. 6), operculum is present in a few forms of Hygophum, and to a lesser extent in E. rissoi. The palatine teeth Myctophum, and Symbolophorus; a maxillary shelf of other species of Electrona and also Protomyc- is absent in Diogenichthys and some Benthosema tophum show a variation between small and moder- and Hygophum; and the ventral area of the pos- ately enlarged; all species of the subgenus Hierops terior portion of the maxillary is widely expanded do not have notably enlarged palatine teeth, as in Electrona, Benthosema, and Hygophum. The suggested by Wisner (1963b: 25 ) . The elevated total variation gives the impression that Hygophum, PO, of Metelectrona is also found in Electrona Myctophum, and Symbolophorus are more closely paucirastra and to a lesser extent in E. subasper. related to each other than to the other three genera; The only distinguishing character for Metelectrona certainly Myctophum and Symbolophorus are more is the elevated VO„ a feature also present in Dio- closely related than any other two of the genera. genichthys and Benthosema, but in no member of The photophore patterns of the genera are some- the genus Electrona. Becker (1963) described what more instructive. In Benthosema and Dio- Electrona ventralis, in which the only distinguish- genichthys, the VO, is elevated, as in some species ing characters from all other species of the genus of Electrona, while the PVO photophores are were the elevated VO, and two raised AO photo- horizontal, as in Protomyctophum. In Hygophum, phores. Future work may show that E. ahlstromi Myctophum, and Symbolophorus, the VO photo- and E. ventralis are synonymous. Few differences phores are level or slightly arched and the PVO are evident in the original descriptions. In the photophores are inclined. The supracaudal glands absence of any other diagnostic characters, I con- of male Diogenichthys, Hygophum, and some sider the elevation of the V02 to be of specific, but Benthosema are single organs margined with black not of generic, significance and regard Metelec- pigment; although not as well developed, they are trona as a synonym of Electrona. E. ahlstromi similar to the supracaudal glands of members of and/or E. ventralis are not far removed from other the subgenus Hierops. If the adult characters in species of Electrona, and appear to be the continua- Protomyctophum are all considered primitive, then tion of an evolutionary trend commencing with Symbolophorus can be considered the most ad- E. antarctica and E. carlsbergi and continuing vanced genus of the tribe, as it is most unlike through E. subaspera and E. paucirastra. E. rissoi Protomyctophum. Myctophum and Hygophum are is an extremely deep-bodied, foreshortened form more closely related to Symbolophorus than to which is the most specialized of the genus; it is Protomyctophum or Electrona, yet each genus has also the only species which occurs in the northern some representatives with some primitive charac- hemisphere. I am in complete agreement with Wis- ters. Benthosema is most similar to Electrona, dif- ner (1963b: 27 ) regarding the status of the sub- fering only in the position of the PLO and Pol. genus Elampa, erected by Fraser-Brunner (1949) The supracaudal glands in some species resemble for E. subasper. This form is not representative of those of Diogenichthys and Hygophum, while other an independent line of evolution, particularly in species resemble Electrona in this character. Dio- light of the subsequent discovery of E. paucirastra genichthys resembles Benthosema in the fusion of and E. ahlstromi; Elampa is considered a synonym the third circumorbital and the elevated V02, but of Electrona. differs in having a well-developed orbital process The remaining five genera of the tribe Myc- on the hyomandibula, the specialized dentition, and tophini, Benthosema, Diogenichthys, Hygophum, the lack of a widely expanded posterior portion of Myctophum, and Symbolophorus, are closely re- the maxillary. Diogenichthys consists of diminutive lated and, with Electrona, form a complex group. species; none attain a standard length of 30 mm. With the exception of the highly modified jaw teeth Although differential development may modify 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 65

some features, the skeleton of these small fishes is are present in M. affine. Although the variation of relatively well ossified. Hygophum resembles Ben- this character has not been examined in other thosema in the lack of a well-developed orbital groups of myctophids, the toothless vomer of process and the presence of a widely expanded Ctenoscopelus appears merely to be at one end of maxillary, but shares with Myctophum and Sym- a broad spectrum of variation within the genus bolophorus a number of other characters. Hy- Myctophum. The vertical through the origin of the gophum is the only member of the tribe, and in- anal fin in Ctenoscopelus is just slightly forward of deed the subfamily, to have two Pol photophores the posterior end of the dorsal fin base; in some consistently. The only difference between Myc- species of Myctophum the anal origin is noticeably tophum and Symbolophorus is the position of the behind the end of the dorsal base. The anal origi- first SAO photophore. The position of this organ is nates directly underneath the posterior end of the variable in a number of other groups within the dorsal base in other forms. The difference between family; it is often used as a specific character Myctophum and Ctenoscopelus in this character within one genus. I do not think that the position is slight. All species of Myctophum have the last of such a variable photophore is enough evidence PO photophore slightly raised to the level of the to support the hypothesis of a monophyletic line first pelvic ray, as does Ctenoscopelus. The last PO of evolution. However, Moser and Ahlstrom (1970) of C. phengodes is raised slightly less than that of have indicated that all the larvae of the Symbo- most species of Myctophum; however, the differ- lophorus species which they examined trenchantly ence between C. phengodes and M. brachygnathum differ in the shape of the body and pectoral fin from is less than half the diameter of the photophore. the larvae of Myctophum. Such evidence strongly The only osteological difference found between C. supports a single line of evolution, and primarily phengodes and the species of Myctophum is the for this reason I recognize the genus Symboloph- very slight development of the orbital process of orus. Another line of evidence suggesting that this the hyomandibula in Ctenoscopelus. As suggested genus is monophyletic is that some characters above, the development of an orbital process is but which show variability within the genus Myc- one aspect of the major evolutionary shift of jaw tophum are constant in all forms of Symboloph- elongation. Taken by itself, I do not consider the orus (see Tables 1-9). If the larval morphology is presence or absence of an orbital process to be indicative of generic relationships for this group, significant at the generic level. All other characters the position of one photophore gains considerable of Ctenoscopelus listed by Fraser-Brunner (1949) significance as an indicator of evolutionary lines. are either at one end of a trend of variation within Fraser-Brunner (1949) erected the genus Cteno- scopelus for the placement of a single species, C. Aas phengodes. This form was stated to differ from 0 04s 40' eg" 0 ` + ' s s s° , ° tpe Myctophum by the toothless vomer, the lack of tic AS oi"' ode' .cet tfe +A elevation of the last PO photophore, the more for- ward position of the anal fin, and the strong arma- ture of the opercle. He also stated that Ctenoscope- lus has a broad maxillary, while that of Myctophum is narrow. The posterior portion of the maxillary is no broader in C. phengodes than in M. brachy- gnathum; the maxillary in all species of Mycto- phum, like those of Symbolophorus and Diogenich- thys, is moderately broadened posteriorly, less broad than those of other genera within the tribe, but broader than those found in all other tribes. The upper part of the opercle of M. brachygnathum, M. lychnobium, and M. aurolaternatum is dentate. That of M. lychnobium is as strongly dentate, or more so, than the opercle of C. phengodes. In M. brachygnathum, M. asperum, and M. lychnobium, a patch of very small teeth is present on each side of the head of the vomer. However, in M. auro- laternatum, M. nitidulum, and M. affine each patch FIGURE 19. Generic relationships within the tribe is reduced to a few teeth; two to three small teeth Myctophini. 66 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

differences in vertical distribution may account for some of the ecologic divergence, specific differ- ences in life habits certainly exist which are not reflected in morphology. The same is apparently true at the generic level. This problem and the as- sumed parallel evolution of some genera make analysis of the evolutionary relationships difficult, and certain lines of the phylogenetic diagram (Fig. 19) are equivocal. It could be argued that the Benthosema-Diogenichthys line diverged from Protomyctophum and the Hygophum-Myctophum- Symbolophorus line split off from Electrona. Future work may clarify these uncertainties. Gonichthyini. The four genera of the tribe Gonichthyini are easily divisible into two evolu- tionary lines, Loweina and Tarletonbeania, and Gonichthys and Centrobranchus, as noted by Bolin (1939), Fraser-Brunner (1949), and Moser and Ahlstrom (1970) (Fig. 20). In Loweina and Tar- letonbeania, the nasal is concave with a slight ven- tral ledge, the first circumorbital has an ethmoid process and no anterior ledge, the lateral shelf and FIGURE 20. Generic relationships within the tribe posterior plate of the third circumorbital are com- Gonichthyini. pletely fused, the premaxillary teeth are small and conical, the second epi- and pharyngobranchials the species of Myctophum or are not definitive for are not reduced, the teeth of the third pharyngo- C. phengodes. One apparent photophore difference branchial are small and conical, there are three is the elevation of the second Prc to near the lateral dorsal and two ventral hypurals, the PLO is oppo- line in C. phengodes. However, this does not make site the pectoral base, the males have a large, single Myctophum phengodes distinctive enough to merit supracaudal gland and the females have no caudal a monotypic genus. lumious glands. In Gonichthys and Centrobranchus As Fraser-Brunner (1949) pointed out, various the nasal is convex with no ventral ledge, the first degrees of ctenoid scales occur in the genus Myc- circumorbital has an anterior ledge and no ethmoid tophum. Those forms with strong ctenoid scales process, the lateral shelf and posterior plate of the have no other character which unites them, and the third circumorbital are partially fused, the pre- subgenus Dasyscopelus of Gunther (1864), based maxillary teeth are moderately or strongly hooked, upon the presence of ctenoid scales, is not recog- the second epi- and pharyngobranchials are re- nized. It should be pointed out that no sets of char- duced, the teeth of the third pharyngobranchials acters differentiate any grouping of the seven are modified as pegs or plates, there are one or two species of Myctophum examined. dorsal and one ventral hypurals, the PLO is just The five genera Benthosema, Diogenichthys, Hy- dorsal to the upper edge of the pectoral base, and gophum, Myctophum, and Symbolophorus have the infracaudal luminous glands in females and apparently radiated from a Protomyctophum- supracaudal luminous glands in males are a series Electrona stock, and parallel evolution within the of small, non-overlapping organs. The premaxillary groups has resulted in a mosaic distribution of and pharyngobranchial teeth modifications, reduc- characters. Apparently few morphological charac- tion of the second epi- and pharyngobranchials, ters are correlated with the ecologic specializations fusion of the hypurals, and modification of the nasal necessary for a radiation resulting in many species. of Gonichthys and Centrobranchus are specializa- In most cases, we are not even aware what these tions that indicate Loweina and Tarletonbeania are ecologic specializations are. At Eltanin station more similar in adult morphology to the primitive 1337, all seven species of Protomyctophum that ancestor than are the former two genera. The de- are known from subantarctic waters were taken in velopment of an ethmoid process of the first cir- one midwater trawl. Yet the only morphological cumorbital in the latter two genera is presumably differences between the species are minor ones in a specialization that parallels the conditions found meristic counts and photophore patterns. While in most Lampanyctinae. The complete or incom- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 67 plete fusion of the third circumorbital is a variation Lampanyctini. The tribe Lampanyctini consists which has occurred in a number of groups. Com- of eight genera, which can be grouped in three lines plete fusion is apparently the primitive state, for it (Fig. 21). Taaningichthys and Lampadena are also occurs in the primitive members of the tribe closely related, as are Stenobrachius, Lampanyctus, Myctophini. Although the loss of the dorsal extra- and Triphoturus; Bolinichthys, Lepidophanes, and scapular in Loweina is a distinct specialization, the Ceratoscopelus form the third group. Certain char- presence of two Prc photophores, a coracoid fenes- acters indicate that the Taaningichthys-Lampadena tra, and the lack of an ossified basihyal are charac- line is the most primitive of the tribe, since these ters that indicate Loweina is more primitive than features are found in a number of other tribes. Tarletonbeania. Taaningichthys has jaws of moderate length and Centrobranchus is obviously more specialized unfused procurrent caudal rays, characteristic of than the closely related Gonichthys. Most of the many members of the subfamily Myctophinae; the distinctive characters of Centrobranchus are at one split lateral shelf of the third circumorbital and the end of a grade from the ancestral state, with Gon- curved outline of the fifth circumorbital of Lampa- ichthys showing the intermediate condition. Thus, dena are features found in no other genus of the the pharyngobranchial teeth in Gonichthys are tribe, but in a number of species in other tribes of modified as pegs, in Centrobranchus they are plates; the subfamily. The extensive orbital shelf on the the nasal is more heavily ossified and more ex- fourth circumorbital of Lampadena is usually found panded posterolaterally in Centrobranchus than in only in the primitive subfamily Myctophinae. The Gonichthys; hypural fusion in Gonichthys has re- presence of different primitive characters in each sulted in two dorsal and one ventral elements, while genus indicates that the two genera have specialized in Centrobranchus one dorsal element and one ven- in different ways since their divergence; however, tral element are present. These characters, and the the common characters between Taaningichthys lack of gill rakers, indicate that Centrobranchus is and Bolinichthys suggest that Taaningichthys may one of the most specialized genera within the entire be more primitive than Lampadena. The two de- family. scribed species of Taaningichthys are among the Notolychnini. The relationships of Notolychnus deepest dwelling of all myctophids; collections indi- and the position of the tribe Notolychnini have cate that they are one of the few groups of lantern- been outlined above fishes which do not undertake a vertical migration. The greatly decreased size of body photophores, and possibly the variability of these organs, may be t.:' ,,,0* ''' •- related to the deeper bathypelagic environment. ,OS. , E., 0*. , ' The spectacular development of the caudal lumi- nous glands, and their similar morphology in both genera, is one feature that indicates a close rela- tionship between Lampadena and Taaningichthys. Although a number of osteological differences were found between the two genera, only one species of Lampadena, L. urophaos, was available for study. Recent work (Nafpaktitis and Paxton, 1968) has shown that L. urophaos is one of the most advanced species in the genus; a future examination of the skeleton of a species like L. chavesi, which is more similar to Taaningichthys, may show that the distinctions between the genera are not great and definitive characters may be hard to find. Lampadena was first formally described by Goode and Bean (1896:85) with Lampadena speculigera as the type species by monotypy. How- ever, Whitley (1968) has recently shown that the generic name was first published by Gill (1893: 113, 123), who ascribed its authorship to Goode and Bean, and pointed out their intention of pub- lishing the new genus. However, since Gill pub- FIGURE 21. Generic relationships within the tribe Lampanyctini. lished the name in combination with Scopelus par- 68 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. 13 vimanus (Giinth.?) Hutton, 1872, Lampadena dentigerous area on the anterior portion of the pre- satisfies the conditions of Article 16 a v (Anon., maxilla in Bolinichthys suggest both the primitive 1961), and is an available generic name. Citation nature of this genus and a relationship to the Taan- of the genus should therefore read Lampadena ingichthys-Lampadena line. The long dorsal expan- Goode and Bean in Gill, 1893. W. I. Follett sion on the posterior portion of the maxillary, the (personal communication) has pointed out that the presence of the hyomandibular foramen in the available specific name is in fact a species inquir- anterior head of that bone, and the presence of enda, for Hutton's (1872) citation reads "Scopelus luminous tissue on the body are features shared by parvimanus Giinth.?"; as such this species cannot Bolinichthys, Lepidophanes, and Ceratoscopelus, be considered the type species of the new genus, and not found in any other genus in the tribe. as indicated by Article 67 h (Anon., 1961), and Bolin (1959) recognized the two evolutionary lines the genus Lampadena, for purposes of type fixa- within Lepidophanes (sensu lato) and stated "It tion, must be regarded as originally published with- would be perfectly logical to consider these two out included nominal species. Therefore the type lines as separate genera but, since the relatively few species, by subsequent monotypy, is Lampadena species involved do not constitute an unwieldy unit, speculigera, as the first species subsequently re- it seems advisable to leave them together for the ferred to the genus (Goode and Bean, 1896), as present." Although I have studied the skeletons of provided by Article 69 a ii 2 (Anon., 1961). only L. longipes and L. guentheri, I have seen speci- Recently Coleman and Nafpaktitis (1972) de- mens of three other species, L. gaussi, L. supralater- scribed a new genus of myctophid, Dorsadena, on alis, and a species close to, if not conspecific with, the basis of one new species from the eastern North L. blacki. As Bolin pointed out, L. guentheri and Pacific. The long jaws, sculptured circumorbitals, L. gaussi are in one line, with the other three secondary photophores, and four to five Prc photo- species in the other. L. gaussi has the peculiar hooks phores are indicative of phylogenetic placement on the posterior margin of the ventral procurrent within the subfamily Lampanyctinae, while the rays found in L. guentheri, while the other three single, large, translucent dorsal and ventral caudal species have normal procurrent rays (see Fig. 15). luminous glands and photophore arrangement In addition, L. gaussi has a long jaw characteristic suggest close relationship to Lampadena and Taan- of L. guentheri. The other two forms have jaws of ingichthys. Coleman and Nafpaktitis have summa- moderate length, extending about one-half an eye rized the characteristics of the three genera, which diameter behind the orbit, a condition similar to include striking similarities in otoliths. Yet Dorsa- the short jaws of L. longipes. The expanded ante- dena possesses a number of unique characteristics rior portion of the premaxillary with enlarged teeth that clearly warrant generic designation and create is also present in the three species of the L. longipes a complex picture of relationships. The additional line. These osteological characters, together with luminous gland anterior to the adipose fin is unique the photophore and luminous tissue differences in the family, as is the presence of a number of listed by Bolin (1959) , are as dissimilar as the secondary photophores associated with each scale. characters of any two closely related genera within Some species of Lam panyctus have a small lumi- the family. I consider the jaw character to be of nous patch at the base of the adipose, while species particular evolutionary significance. There is one of the genera Bolinichthys, Lam panyctus, and further reason for differentiating the two lines. The Scopelopsis with secondary photophores have only group typified by L. longipes has a number of char- one photophore associated with each scale. The acters in common with the Lampadena-Taaningich- position of the last one or two Prc photophores far thys line, namely short or moderate jaws, enlarged above the lateral line is paralleled only in Notolych- dentigerous area on the anterior portion of the pre- nus. An osteological analysis of the genus should maxillary, lack of a keel on the third circumorbital, prove most interesting, for it may indicate a closer extensive orbital shelf on the fourth circumorbital, link of Notolychnus with the tribe Lampanyctini. presence of luminous tissue on the eye, and For the present, the bulk of external morphology the presence of three Prc photophores. The L. suggests that the closest relationships of Dorsadena guentheri lines shares more characters with Cerato- lie with Lampadena and Taaningichthys. scopelus: the presence of a keel on the third cir- Bolinichthys and Stenobrachius are the primitive cumorbital, the lack of an enlarged dentigerous forms of each of the other two lines in the tribe. area on the anterior portion of the premaxillary, While the two genera share some characters, the the presence of hooked procurrent caudal rays, the short or moderate jaws, a well-developed orbital lack of luminous tissue on the eye, and the presence shelf on the fourth circumorbital, and an enlarged of four Prc photophores. Recognition of two dis- 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 69 tinct genera clarifies the pattern of evolutionary in Stenobrachius), and three to six, usually four, relationships within the tribe, and emphasizes the VO photophores (versus four to five in Steno- differences between the two monophyletic lines. brachius, five in Triphoturus, and four in Lam- Therefore Lepidophanes is restricted to the forms panyctus). On the basis of the above characters, a L. guentheri and L. gaussi and Bolinichthys is de- series of evolutionary stages was suggested, start- scribed above as a new genus, with B. longipes as ing with Stenobrachius and leading to Triphoturus the type-species. Nafpaktitis and Nafpaktitis through Parvilux. The placement of Lampanyctus (1969:57) have shown that Alcock's (1891) Sco- in this scheme was not indicated, although in the pelus pyrsobolus is currently indeterminable, and introduction, Hubbs and Wisner (1964:449) state, have used Lampanyctus longipes (Brauer, 1906) "In general the appearance [of Parvilux] is most and Lampanyctus photophorax (Parr, 1928) as like that of the deep-living flaccid species of Lam- names for two of the three species of the Bolinich- panyctus, particularly those with weakly developed thys "pyrsobolus species group" present in the pectoral fins." The genus Lampanyctus includes Indian Ocean. On the basis of their descriptions the about 40 species, which show a wide range of osteological studies described herein were based variation in morphology. The characters that dif- upon B. longipes. ferentiate Lampanyctus and Stenobrachius have Ceratoscopelus is distinguished from both been listed above. The only characters which will Bolinichthys and Lepidophanes by the presence of separate Lam panyctus from Triphoturus are the a level series of PO photophores, reduction of the presence of a small dorsal process on the opercular palatine tooth rows, the lack of any ossified distal head of the hyomandibula and four VO photo- pectoral radials, and the presence of a well- phores in Lam panyctus. However, the two species developed hypural flange. A few characters are of Triphoturus examined have very slender bodies shared by Bolinichthys and Ceratoscopelus, to the and weakly ossified skeletons, as contrasted to the exclusion of Lepidophanes. Ceratoscopelus has a relatively deep bodies and moderate to strong ossi- jaw of moderate length; the lengthening of the jaw fication found in the species of Lampanyctus. Some in Lepidophanes apparently occurred after the di- species of the latter genus are poorly ossified, but vergence of Ceratoscopelus. In addition, Bolinich- only L. idostigma is as weakly ossified as the thys and Ceratoscopelus lack a concave lateral species of Triphoturus. On the other hand, no shelf in the third circumorbital and have no small osteological characters will differentiate Parvilux dorsal process on the opercular head of the hyo- from Lampanyctus, and, with the exception of the mandibula. However, the shared characters of the position of the first SAO photophore, the two circumorbitals, premaxillary, urohyal, and Prcs are groups are inseparable. indicative of a close relationship between Lepido- Bolin (1959) suggested that at least three evolu- phanes and Ceratoscopelus. The relationship is tionary lines are present in Lam panyctus, two of particularly apparent in the development of hooks which were defined on the basis of long or short on the procurrent rays; a graded series (Fig. 15), pectoral fins. In his key to the species of Lam- with C. maderensis being the most specialized in panyctus, Fraser-Brunner (1949) used three major this character, is indicated. groupings: those with cheek photophores and long The line leading to Lampanyctus, largest genus pectoral fins, those without cheek photophores but of the tribe, includes three genera, Stenobrachius, with long pectorals, and those with short pectorals, Lampanyctus, and Triphoturus. Stenobrachius, on which also have no cheek photophores. Most spe- the basis of the number of characters shared with cies with cheek photophores and long pectoral fins Bolinichthys and Taaningichthys, appears to be the also have secondary photophores over the entire most primitive genus. Lampanyctus and Tripho- body or restricted to the area near the lateral line, turus share the following characters which are not and have a small luminous gland at the adipose found in Stenobrachius: fully developed keel on fin. However, this complex of four characters is the third circumorbital, small dorsal expansion on not present in all species; L. pusillus and L. pho- the posterior portion of the dentary, and the uro- tonotus lack the luminous gland at the adipose fin, hyal wing behind the second basibranchial. while L. madconaldi and L. iselinoides have pec- Hubbs and Wisner (1964) described a new torals of moderate length. All the species lacking genus, Parvilux, which is related to this group of cheek photophores also lack secondary photo- genera. Distinctive features of the new genus were phores and a luminous organ at the adipose. In the listed as the slightly angulated SAO photophores present study, 13 species of Lampanyctus were (versus strongly angulated in Triphoturus and examined, including six species with cheek photo- Lampanyctus), two Pol photophores (versus one phores and moderate or long pectorals, three spe- 70 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No. I3 cies with long pectorals and no cheek photophores, like that of the other species of Lampanyctus, but and four species with short to moderate pectorals shows a striking resemblance to the otolith of Cera- and no cheek photophores. Few osteological char- toscopelus. It can be added that the otolith of acters were constant in the individual groups. All Bolinichthys longipes is similar to otoliths of these of the short-finned species, L. regalis, L. ritteri, two forms; the otoliths of Lepidophanes are un- L. achirus, and L. idostigma, were much more available for examination. This resemblance sug- poorly ossified than the other forms; L. macdon- gests that the long-finned species of Lampanyctus aldi, with moderate pectorals, was the most weakly without cheek or secondary photophores may be ossified of the other forms, suggesting some cor- the most primitive of the genus. Although no other relation with the amount of ossification in the skele- Lampanyctus otolith examined is similar to that of ton and the length of the pectoral fins. The three L. parvicauda (those of L. omostigma and L. species with long pectorals and no cheek photo- hubbsi are unknown), a variation of otolith types phores, L. parvicauda, L. omostigma, and L. hubbsi, within the other species is apparent; Lavenberg and differed from all other species by the lack of a Fitch are planning a study of these important ele- strongly concave lateral shelf of the third circum- ments. The otolith of Lampanyctus ingens is most orbital. These three species form a very closely similar to those of the short-finned species. related group (see Wisner, 1963a), and no extrap- Although Stenobrachius appears to be the most olation to the other species with long pectorals primitive of the Lampanyctus relatives, the lines of and no cheek organs should be made without an evolutionary relationships are not clear. I think that examination of at least one of them. No other Triphoturus is probably a derivative from Lam- pattern of osteological variation is discernible. A panyctus, rather than an intermediate between number of characters vary among the species, but Stenobrachius and Lampanyctus. no more than one feature unites the same group Fowler (1925) erected the genus Cyphoscopelus of species. Perhaps future work on more species to contain Scope/us langerhansi (Johnson, 1890). will be able to define adequately the evolutionary In the original description of this species, the dorsal lines which have been indicated above. Certainly fin was said to originate over the base of the pec- the present evidence is not sufficient to recognize toral fins, a condition unique in the family Myc- a formal division even at the subgeneric level. tophidae. Fraser-Brunner (1949) thought that the Parvilux is most similar to the species with short original description of the species could apply to pectorals; the only osteological difference is the a Lampanyctus, except for the position of the lack of pectoral fin rays in one of the four species, dorsal fin. On the other hand, the following por- L. achirus. The difference in position in the first tion of the original, and only description is instruc- SAO photophore is significant for other generic tive: "The rictus reaches to about the vertical of groups, notably Symbolophorus; however, Parvilux the posterior part of the orbit." This character appears to be more closely related to the short- limits the number of genera in which the species finned species of Lampanyctus than this species could be placed, if the dorsal fin description is in group is to the group with long pectorals and cheek error; species of Bolinichthys, Diaphus, and a photophores. One other consideration supports the number of genera in the tribe Myctophini are the placement of Parvilux in synonymy with Lampan- only myctophids with such short jaws. Johnson yctus. If the short-finned group is ever recognized (1890) compared Scope/us langerhansi to Alysia as a formal subgenus or genus, the name Nanno- ( =Gonichthys) and stated "In Alysia there is a brachium Gunther (1887), type-species Lampan- single row of silvery spots along the ventral line; yctus niger, not Parvilux, will be applicable. The here there are several rows of silvery spots on the type of Lampanyctus is L. crocoddus, a typical sides." The several rows may refer to the elevated long-finned species with cheek photophores, sec- photophores of a number of series, typical of both ondary photophores, and a luminous gland at the Diaphus and Bolinichthys; genera of the tribe adipose base. The type-species of Nyctimaster Myctophini have no more elevated photophores (Jordan, 1921) is L. jordani, a form which shares than are found in Gonichthys. Johnson presumably the above four characters with L. crocodilus. At referred to the procurrent rays when he mentioned the present state of our knowledge, it is not pos- the spines present before the caudal in Gonichthys sible to break down the genus Lampanyctus into and notes their absence in Scopelus langerhansi. meaningful groups. If the original description is entirely correct, the Lavenberg and Fitch (1966) have pointed out forward placement of the dorsal fin, absence of that the sagitta of Lampanyctus parvicauda is not procurrent rays, and presence of several rows of 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 71

photophores on the side of the body cannot pertain species. Two characters, which may be indicative to a myctophid. A re-examination of the type speci- of close relationship, are restricted to D. luetkeni men, which Fraser-Brunner (1949) did not locate, and D. pacificus. The lateral shelf of the third cir- is necessary for proper familial allocation. cumorbital is concave rather than perpendicular in Diaphini. The tribe Diaphini is represented by both species, and a small dorsal expansion is pres- two genera, Lobianchia and Diaphus. Fraser-Brun- ent on the posterior portion of the dentary. Both of ner (1949) split the group into four subgenera, these features reach their highest development in while Bolin (1959) recognized three genera, in- the tribe Lampanyctini, particularly in the genus cluding only 27 species of the more than 100 Lam panyctus. In addition, D. luetkeni is the only nominal forms of the group. The subgenera of species of Diaphus examined that has an ethmoid Fraser-Brunner were defined solely on the basis process on the first circumorbital; this feature is of the morphology of the orbital organs. Bolin de- found in all other members of the subfamily Lam- fined Lobianchia on the presence of caudal lumi- panyctinae, including Lobianchia, and in none of nous organs; the definitions of Diaphus and Aetho- the Myctophinae except Loweina and Tarleton- prora included the lack of luminous caudal glands, beania. D. luetkeni and D. pacificus may represent the type of orbital organs, and features of denti- a primitive line within the Diaphus group, although tion. Diaphus (sensu stricto) according to Bolin D. luetkeni has a specialized Vn. (1959), is characterized by the presence of a sub- As has been pointed out, all other variations in orbital light organ and moderately hooked teeth osteology show a mosaic pattern of distribution in the posterior portion of the premaxillary. Aetho- among the species. With the exception of D. theta- prora lacks a suborbital organ and has a greatly D. mollis and D. luetkeni-D. pacificus, no more expanded Vn and an inner row of enlarged teeth than one osteological character is unique for any on both jaws. Nafpaktitis (1966) has pointed out grouping of species. A solution to the problems of that the hooked teeth of Diaphus (sensu Bolin) are species relationships and superspecific groupings not a definitive character, in that intermediate requires a study of much more extensive material forms between hooked and conical teeth occur. than has been available here. In the future the It may be noted that hooked teeth are not unique group surely will be split into several subgenera to the tribe Diaphini; they occur in different areas or genera, if but for convenience alone. Only two of the jaws in genera of the tribes Myctophini, evolutionary lines within the group are indicated Gonichthyini, and Lampanyctini also. In the pres- by the osteological variation, but the evidence and ent study, only 11 species of Diaphus were avail- the sample are too meager to consider the recogni- able for clearing and staining: two species, D. theta tion of superspecific categories. It must be admitted and D. mollis, referred to Diaphus (senus stricto) that the difference in jaw length between D. theta by Bolin; four species. D. metopoclampus, D. os- and D. mollis and the other species examined is tenfeldi, D. elucens, and D. fragilis, referred to supportive of Bolin's recognition of the genus Aethoprora; and five others. Such a sample is a Diaphus (sensu stricto). But D. lewisi (=D. van- poor representation of the fifty or more species in hoeffeni) has a suborbital organ, hooked teeth, and the group. However, the osteological variation seen a long jaw; the fusion of the Dn and Vn also indi- in this sample is considerable, although no con- cates the intermediate position of this species be- sistent patterns are apparent. The presence of short tween the Diaphus (sensu Bolin) and Aethoprora or moderate jaws, extending half an orbital diam- groups (Nafpaktitis, 1966). Another problem is eter or less behind the posterior margin of the orbit encountered if Diaphus is restricted to only those and the lack of a short dorsal expansion on the forms with short jaws. What generic name will all posterior portion of the maxillary separate D. theta other species of the group take until a definitive and D. mollis from all other species examined. study is accomplished? Additional generic taxa D. metopoclam pus and these two species lack a have been formulated in the past, and more prob- fused preopercular flag on the dorsal tip of the lems were created than solved. Stability of nomen- preopercle. D. pacificus and D. elucens have clature will surely not be achieved by a restriction slightly hooked teeth on the posterior portion of the of the genus Diaphus; recognition of additional premaxillary, while these teeth are moderately genera in the group, which currently has five ge- hooked in D. theta and D. mollis. D. theta, D. neric synonyms, should be reserved for the future, mollis, D. elucens, and D. fragilis have the anterior as emphasized by Nafpaktitis (1966: 420) . urohyal distinctly split into two separate heads; The relationship of Lobianchia to any line within the anterior urohyal is but slightly split in all other Diaphus is unclear. The presence of caudal lumi- 72 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 nous glands and a single, small orbital organ anterior portion of the premaxillary; and Hintonia suggests the primitive nature of Lobianchia. The is unique in the lack of a small keel on the fifth presence of an ethmoid process on the first cir- circumorbital and in the presence of a long dorsal cumorbital in both species of the genus and the expansion on the posterior portion of the maxil- concave shape of the lateral shelf of the third lary, a reduced or absent supramaxillary, a small circumorbital in one species may be indicative of dorsal expansion on the posterior portion of the a relationship with D. luetkeni and/ or D. pacificus. dentary, an inner row of enlarged teeth for the However, both latter species have two well-devel- entire length of the dentary, and the extension of oped orbital organs, particularly D. luetkeni, and the basibranchial plate behind the third hypobran- Lobianchia lacks the expansion on the posterior chials. None of the other three genera, Gymno- portion of the dentary. D. dumerili and D. splen- scopelus, Lam pichthys, and Scopelopsis, has any didus are the only species of Diaphus examined osteological character which will differentiate one that have a small keel on the fifth circumorbital, group from all other groups in the tribe. Gymno- as does Lobianchia. But other differences are ap- scopelus, with nine species, shows a wide variation parent and the closest relatives of Lobianchia may of osteological features. Lam pichthys and Scope- not have been examined in this study. Due to the lopsis differ from each other in some osteological considerable variation within Diaphus of all osteo- characters, but neither can be differentiated from logical features noted, the only definitive character all species of Gymnoscopelus. for Lobianchia is the presence of caudal luminous The relationships of the genera within the Gym- glands. noscopelini are not completely clear (Fig. 22). Gymnoscopelini. The tribe Gymnoscopelini While Lam panyctodes is the most primitive genus, shows relationships to the Diaphini through the Hintonia differs from all the rest in the largest num- primitive gymnoscopeline genus Lampanyctodes, ber of characters. No distinct relationship to any as has been shown above. Considering only osteo- member of the tribe is evident and this form appar- logical characters, Lampanyctodes differs from the ently split off the ancestral stock early. Certain pho- other five genera only in the wide ossification of tophore features, such as an elevated VO, are similar the pubic plate; Notoscopelus is the only genus of to Lampanyctodes, while the presence of three Pol the tribe with a moderately developed hypural photophores, cheek photophores, and secondary flange and an enlarged dentigerous area on the photophores suggest a relationship to Lam pichthys. The presence of secondary photophores over the entire body and the lack of extensive patches of luminous tissue are indicative of a close relation-

p‘'..,+" ship between Lam pichthys and Scopelopsis. On the sc ‘ basis of photophore pattern and luminous tissue distribution. Notoscopelus appears to be interme- diate between Lampichthys and Gymnoscopelus. Due to the great variability of the osteological characters in the genus Gymnoscopelus, its rela- tionships are unclear. On the basis of photophores, the genus appears to be similar to the ancestral stock of Notoscopelus and the Lampichthys-Scope- lopsis line. The characteristics of larval morphology and the level arrangement of the PO photophores has prompted Moser and Ahlstrom (personal com- munication) to suggest a relationship between Ceratoscopelus and Notoscopelus. But a direct comparison of the two forms reveals a number of differences (see Tables 1-10). While many of these character differences are too variable within the family to be considered of major evolutionary im- portance, the presence of the following characters supports the placement of Notoscopelus within the FIGURE 22. Generic relationships within the tribes Diaphini and Gymnoscopelini. tribe Gymnoscopelini: long jaw, a supramaxillary, 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 73

curved fifth circumorbital with a keel, two to three groups are known. Also, the position of one photo- tooth patches on the first pharyngobranchial, short phore is the only feature of adult morphology that ischial ligament, a Dn, upper PVO above the pec- differentiates members of the genus Symbolophorus toral base, and ten to fifteen procurrent rays in the from Myctophum, and the larval morphology of dorsal and ventral series. Notoscopelus is the only the groups is indicative of evolutionary divergence. member of the Gymnoscopelini to have a well- Although the larvae of the species of Gymno- developed hypural flange and an expanded anterior scopelus are undescribed, the position of one pho- area on the premaxillary, although no enlarged tophore may be as indicative of monophyly in this teeth are present. These two characters are also group as in Symbolophorus; I therefore recognize present in some forms of the Lampanyctini, but Nasolychnus at the subgeneric level. since Lam panyctodes and the other gymnoscope- Gunther (1873) introduced Gymnoscopelus lines lack the characters, they have presumably when he described a new species, G. aphya. The developed independently in Notoscopelus. description of the species was inadequate, as nearly Gymnoscopelus, with nine species, is the most all descriptions of that time were, and Bolin re- speciose genus in the tribe. As in Diaphus, the cently found that Lampanyctus nicholsi Gilbert orbital organs show a great variation in shape, (1911) is conspecific with Giinther's species, a although none are as well developed as in some fact which Bolin communicated to Andriashev. forms of Diaphus. The orbital organs are often Andriashev (1962) suggested that since G. aphya specifically distinct and sexually dimorphic in both had not been generally used, it should be consid- genera. Also like Diaphus, Gymnoscopelus lacks ered a nomen oblitum; Fraser-Brunner (1949) had any caudal luminous glands. Although the eco- used the name, but for the wrong species. Three logical significance of well-developed orbital or- points mitigate against this suggestion. First, the gans is unknown, their presence in both Gymno- species is not a common one and has rarely been scopelus and Diaphus suggests that the orbital reported in the literature. Andriashev cited only organs play an important part in the radition of a two references to G. nicholsi besides the original group. description, and both of these included more than Andriashev (1962) resurrected a subgenus, Na- one species under the name. Second, G. aphya had solychnus, described by Smith (1933), for those been used in the fifty years prior to Andriashev's species of Gymnoscopelus with the upper PVO work, by Fraser-Brunner, albeit for the wrong above the base of the pectoral fin. The specific species. Finally, the species in question is the type names in the genus are in a chaotic state (Andria- of Gymnoscopelus and as such should stand with shev, 1962). However, the unpublished work of the genus. I consider Gymnoscopelus nicholsi (Gil- Richard F. McGinnis, on the Gymnoscopelus from bert) a junior subjective synonym of Gymno- the Eltanin collections, have revealed that five scopelus aphya Gunther, the type of the genus. distinct forms have the upper PVO above the pec- toral base. Three names are available for this THE EVOLUTIONARY SIGNIFICANCE group, but matching species to names can only be OF PHOTOPHORE PATTERNS accomplished by a re-examination of the type The stated purposes of the present study are to material. No osteological characters will differen- describe osteological variations within the family tiate forms of the two subgenera, and the only Myctophidae, to broaden the definitions of the difference is the position of the PVO photophore. evolutionary lineages to include characters of os- While the position of one photophore is not strong teology, to determine the major evolutionary trends grounds for the recognition of a formal superspe- within the family, to assess the relationships of the ciflc category, certain considerations suggest that various evolutionary lineages, and to examine the Nasolychnus be accepted at least at the subgeneric significance of photophores in the evolutionary level. The position of the upper PVO photophore history of the family. To accomplish the last objec- in relation to the pectoral base is constant within tive, the previous ideas on the evolutionary history the other genera of the tribe, being above the base of the family, which have been based primarily on in all forms of Notoscopelus and Lam pichthys, photophores, must be briefly compared to the con- opposite the base in Hintonia and the four species cept of evolutionary relationships presented above. placed in the subgenus Gymnoscopelus, and below A large number of skeletal characters were defined the base in Lam panyctodes. An evolutionary series and analyses of both osteological features and of species is not indicated by the characters exam- luminescent organs, including tissue other than ined and no intermediates between the subgeneric photophores, resulted in the phylogeny presented. 74 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13 Since my ideas of the evolutionary history of lan- Fraser-Brunner thought that the modification of ternfishes differ somewhat from those of other the procurrent caudal rays from soft flexible ele- workers, a comparison of phylogenies may give an ments to stiff spines was a nodal point in the evo- indication of the significance of photophore pat- lution of the family. I have found this character terns in the major evolutionary shifts among involved in a graded series from the primitive con- myctophids. dition, where the two halves of each ray are un- Previous studies did not recognize tribal or sub- fused for their entire lengths, to the most advanced familial categories for the various myctophid condition, where the halves are completely fused groups; however, early works recognized few ge- for most of their lengths; intermediate conditions neric or subgeneric taxa. Brauer (1906), Taaning with only the tips of the rays fused are common in (1918), and Parr (1928) placed all species in the a number of groups. While stiff procurrent rays genera or subgenera Myctophum, Diaphus, Lam- are clearly a specialization found in some advanced padena, Lam panyctus, and Scopelopsis. Mycto- lineages, the gradual change from the primitive phum included all forms here placed in the sub- condition does not appear to be a major adaptive family Myctophinae plus Notolychnus; Diaphus shift within the evolutionary history of the family. represented the tribe Diaphini, and Lam panyctus In my view the major evolutionary advance included the rest of the subfamily Lampanyctinae within the family has been the lengthening of the except for Lam padena and Scopelopsis. These lat- jaws behind the orbit, from a primitive condition ter two genera are small groups; Lampadena in- in which the jaws end under the posterior margin cluded species now placed in Taaningichthys and of the orbit, to the most advanced condition, where Lam padena, and Scopelopsis is monotypic. Bolin the jaws extend more than two eye diameters be- (1939) presented a phylogenetic diagram for the hind the orbit. This shift is doubtless correlated genera and species then referable to the genus with feeding efficiency, and is the most important Myctophum. He recognized eight nominal genera character separating most species in the two major and subgenera in four major lines. Notolychnus evolutionary groups, designated as subfamilies in represented one of the lines, the slender-tailed the formal classification. genera were placed together as a group, and the My recognition of the close relationship between species of Electrona (now in two genera) were the Diaphini and Gymnoscopelini is the only differ- placed apart from the remainder of the forms ence between the pattern of evolutionary lineages under consideration. While Fraser-Brunner (1949) above the generic level developed by Fraser- did not recognize formal subfamilial or tribal cate- Brunner and that described here. The Diaphini and gories for the family, he presented an evolutionary Gymnoscopelini differ in the morphology of the diagram for all genera and discussed their relation- procurrent rays, but agree in most instances in the ships. He considered the four genera of the Gon- lengths of the jaws. Moreover, the photophore ichthyini to be closely related, as he did the genera pattern of Lampanyctodes is intermediate between of the Myctophini; following Bolin (1939), he the typical patterns of the two groups. It is appar- considered Protomyctophum and Electrona primi- ent from the above summary that the changes in tive genera and placed them somewhat apart from photophore patterns closely parallel the shifts in the other genera in the tribe. He discussed the other morphological features within the various controversial position of Notolychnus and placed evolutionary lineages that have been described in its divergence near the base of the Lampanyctinae. the previous section. Diaphus and Lam panyctodes were also thought to The most comprehensive treatment of generic have arisen from the same stock. Although it is not relationships is also that of Fraser-Brunner (1949). apparent from his evolutionary diagram, Fraser- As with the suprageneric lineages, our ideas on the Brunner placed Lam panyctodes at the base of the evolutionary history of the generic groups are in radiation of the Gymnoscopelini. The genera now close agreement. The minor differences in view- placed in the Lampanyctini were thought to have point can be noted by comparing the phylogenetic arisen independently from the Gymnoscopelini. diagram of Fraser-Brunner (1949: 1035) with Fig- From this brief summary, it is apparent that the ures 18-22. My interpretation is that Hygophum major evolutionary lineages discussed in this paper is more closely related to Myctophum than to any were recognized by earlier workers, although a other genus of the tribe Myctophini; Tarleton- higher classification was never presented. In most beania is most closely related to Loweina; Lam- features, the results of this study agree with the panyctus, Ceratoscopelus, and Lam padena arose conclusions of Fraser-Brunner (1949). However, from a common ancestor; and Lam pichthys and 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 75 Scopelopsis form a generic pair. These minor dif- primarily for two reasons. Firstly, the overall pic- ferences do not overshadow the striking similarities ture of the family Myctophidae is of a large num- in the evolutionary conclusions of Fraser-Brunner ber of species, each with a distinctive pattern of and myself. The phylogeny proposed by Moser and photophores. Even in those genera without dis- Ahlstrom (1970) on the basis of larval character- tinctive orbital organs, many of the species are dif- istics is in most particulars identical with that pro- ficult to distinguish on photophore pattern alone; posed herein; the only major difference is the place- use of any key to species will quickly elucidate this ment of the four slender-tailed genera. fact. Coupled with this misconception is the pau- The close agreement at all levels in the phylog- city of observational data on photophore lumi- enies is definitive evidence that photophore pat- nescence regarding color, intensity, pattern, or terns are indicative of evolutionary history, at least number of luminescing organs. in the family Myctophidae. Although Fraser- Scattered throughout the literature, however, Brunner also used characters of the procurrent are a few indications that each of the possibilities rays, median fin positions, dentition, and scales, listed above may be functional in myctophids. Al- his phylogeny is based in large part on the changes though interpretations of color are highly subjec- in photophore patterns. As was pointed out in the tive, a number of hues have been attributed to introduction, the changes of such a plastic set of lanternfish luminescence. Beebe and Vander Pyl characters as photophores seem a priori to be a (1944) record the following colors: Myctophum questionable base upon which to establish the affine, yellowish green; M. aurolaternatum, faint evolutionary history of a group. However, the evo- bluish; Myctophum (=Gonichthys) coccoi, green- lutionary significance of these distinctive organs is ish to turquoise green; Lampanyctus omostigma, extensively supported by the osteological analysis white; L. elongatus (=Notoscopelus resplendens), reported here. pinkish. Bolin (1939) has recorded a pale greenish The functions of photophores in myctophids are light from Myctophum (=Symbolophorus) califor- open to speculation, as few observations and almost niense and a strong blue light from the caudal no experimental data are available. For conve- glands of Lampanyctus (=Stenobrachius) leucop- nience, the luminous tissue of lanternfishes can be sarus and Lampanyctus ( = Triphoturus) mexicanus. broken into five categories: primary photophores, Ohshima (1911) described a blue light from Dia- caudal luminous glands, orbital organs, secondary phus watasei. Beebe and Vander Pyl (1944) have photophores, and luminous patches that do not even indicated that the color of luminescence in M. have the organization of discrete glands or photo- coccoi changes with differences in light intensity; phores. McAllister (1967) has given the latest the greenish light of bright luminescence becomes summary of hypothetical functions for luminous turquoise green as intensity diminishes. Gilbert tissue in fishes. These include interactions both (1915) indicated that the photophores themselves intra- and interspecifically, with a number of pro- differ in color in freshly caught specimens; in two posed functions in each category. closely related species of Lampanyctus (=Steno- As the body photophores in myctophids are brachius), L. leucopsarus had golden yellow pho- often specifically distinct, intraspecific functions tophores while L. nannochir had claret-colored are suggested. However, the differences in photo- organs. phore placement are often subtle in closely related The subjectivity of color interpretation is diffi- species of the same genus, and it is difficult to cult to overcome. My own observations on a num- imagine that swimming fishes are able to recognize ber of species, including Symbolophorus boops off the differences in pattern, even though the eyes of Chile, Myctophum nitidulum off Florida, and M. midwater fishes may be 10 to 100 times more sen- spinosum, Benthosema fibulatum, and Diaphus sitive than those of humans (Clarke and Denton, regani off New Guinea, indicate all luminescence 1962). Such a difficulty would be overcome if was blue-green. The only recorded color emission closely related species displayed one or more of of a lanternfish, Myctophum punctatum, measured the following specializations in photophore lumi- blue light with maximum emission at about 470 mu nescence: differences in color of the light emitted, (Nicol, 1960). Such a color range is expected, as differences in the number of photophores which this is the predominant color of the remaining are illuminated at any given time, or differences in sunlight at midwater depths and the eyes of mid- the intensity and/or a system of flashing off and water fishes should be most sensitive to this area on, similar to firefly flashes. These potentials have of the spectrum (Marshall, 1954; Clarke and Den- not been given detailed consideration in the past ton, 1962). 76 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

It is apparent that in view of the observations luminescence thus expanded, effectiveness in infra- recorded above, spectrographic analysis of lantern- specific interactions is still indicated, and specific fish luminescence should be extended to more spe- recognition remains the most plausible function of cies in other genera. If differences are apparent, body photophores. perhaps they can be correlated to color differences The only observations of luminescence in myc- in the photophores themselves. The limited obser- tophid caudal glands suggest they are used to star- vations, although subjective, indicate that color tle, blind or divert predators (Beebe and Vander could be important in intraspecific interactions in- Pyl, 1944; Bolin, 1961) . The organs are sexually volving lanternfishes. dimorphic in most members of the Myctophinae, Beebe and Vander Pyl (1944) give the only but few of the Lampanyctinae. A dual function of indications that individual photophores may be the organs is probable in the Myctophinae; neither illuminated differentially. They described one morphology nor limited observations give any dying Myctophum affine in which light was emitted indication of the reproductive behavior of the from only the first pair of Br photophores. A speci- Lampanyctinae. men of Lampanyctus macropterus twice displayed The orbital organs are most striking in species flashes from only sets of four or six photophores. of the tribes Diaphini and Gymnoscopelini. One In a dying individual of the same species, all the dying individual of Diaphus regani from off New Br organs and the first pair of PO photophores Guinea was seen to emit weak luminescence from were the brightest. Although their observations on these organs, but none from the body photophores. four other species and my own on the five species Therefore, it appears that the orbital organs, like listed above gave no indication of an ability to the caudal glands, are independent of the control illuminate a limited number of the total comple- of the body photophores, as observed by Ohshima ment of photophores, Ray (1950) has shown that (1911). Since most species of Diaphus have dis- all body photophores are innervated by branches tinctive orbital organs and many have similar pat- of the spinal nerves. Thus, there appears to be no terns of body photophores (see Nafpaktitis, 1968), physiological barrier to nervous control over dis- one may ask why there are different patterns of crete sets of photophores. body photophores in Diaphus, and indeed why Observations on the intensity of luminescence have not these organs regressed or become com- are also greatly limited. Beebe and Vander Pyl pletely lost. Probably photophores were important (1944) as well as Ohshima (1911) have observed in species recognition before orbital organs became some indication of increased intensity in the form highly differentiated and their retention in different of "sparks" or intense flashes from all the body patterns is a result of the previous function. The photophores. Most observations, including my own, lack of degeneration in Diaphus may indicate that indicate a constant illumination diminishing slightly body photophores have more functions than spe- as death approaches. Even these suggest that pho- cies recognition, even in present day forms. tophores are not just either off or on, but some con- Secondary photophores and luminous patches trol of intensity is present. Nicol (1958) measured on the head and body are restricted to species in the intensity of light emitted in approximately the subfamily Lampanyctinae, and are most highly 0.5 second flashes, made up of a series of pulses; developed in species of the tribes Lampanyctini occasionally a burst of flashes of three to four sec- and Gymnoscopelini. No observational data could ond duration was recorded. In addition, prelimi- be found for lanternfishes with this type of lumi- nary records of Ceratoscopelus warmingi from off nous tissue; although Ceratoscopelus warmingi has New Guinea have indicated more rapid flashes are numerous patches of luminous tissue in addition possible. Although the measurements must be veri- to the primary photophores and caudal glands, fied, as dinofiagellate flashes were not ruled out by which type or types of tissue causing the recorded a control, photomultiplier records of flashes were pulses described above was not ascertained. Re- obtained, most showing paired pulses averaging cently Nafpaktitis and Nafpaktitis (1969) have 45 milliseconds duration separated by a period of described variations in the luminous tissue patterns darkness averaging 160 milliseconds. Thus, each in populations of Ceratoscopelus and Lepidophanes species may have its own sequence of flashes, as is (= Bolinichthys). The differences were distinctive commonly found in fireflies (McElroy and Seliger, enough to be accorded specific value, although no 1966) ; the presence of sibling species with different differences in primary photophore patterns were pulse patterns is possible. found. As species of Bolinichthys are sympatric in With the repertoire of myctophid photophore the Indian Ocean, it appears that luminous tissue 1972 OSTEOLOGY AND RELATIONSHIPS OF LANTERNFISHES 77 patches may also function in specific recognition. the major changes that have occurred are the dor- Clearly the major trends of photophore char- sal movement of various photophores, the increase acters must be related to the major shifts and in the number of Prc organs, the extensive devel- adaptive radiation of this successful family. That opment of the orbital organs, and the loss of sexual osteological trends parallel so closely the changes dimorphism in the caudal luminous glands. The in photophore patterns attests to the fundamental development of secondary photophores over the biological significance of the latter in lanternfish head and body, and the apparent reduction of pri- evolution. Although the functions of photophores mary photophores in one form, the development cannot be stated unequivocally, their importance of extensive luminous tissue other than photo- in maintaining the reproductive isolation of species phores, and the complete loss of caudal luminous is indicated, in myctophids at least, by the great glands are all specializations that are only found diversity of photophore patterns. It may be reason- in some of the advanced lineages within the family. able to assume that photophores evolved under a While the significance of some morphological different set of adaptive pressures in the ancestral differences are conjectural, the adaptive signifi- stock of lanternfishes prior to colonization of the cance of the difference in one set of photophores midwater environment. Since all myctophid body is virtually impossible to ascertain. Even if one photophores apparently migrated from a single assumes that species recognition is the primary ventral row (Ray, 1950) , the original selective present-day function of photophores, why should advantage may have been for countershading, as an increase in the number of Prc photophores par- proposed by Clarke (1963). It seems probable that allel the lengthening of the jaws? Of what possible a major adaptive shift in photophore function to adaptive advantage is a lateral position of the that of species recognition has resulted in the radia- PLO photophore to the slender-tailed species of tion of lanternfishes seen today. the tribe Gonichthyini? Answers to these questions A limited number of evolutionary trends in the are not apparent. Perhaps the radiation of species family Myctophidae were described above. To in the genus Diaphus is not causally related to the summarize, from the generalized stock of the tribe proliferation of luminous orbital organs; these or- Myctophini arose the streamlined group of slen- gans may be by-products of the evolutionary history der-tailed forms placed in the tribe Gonichthyini. of the group, that is, the orbital organs may func- Most of the osteological specializations of this tion in the reproductive isolation of species but the group seem to be adaptations for rapid swimming. radiation was due to some other morphologic spe- The subfamily Lampanyctinae is characterized by cialization which offered the group an adaptive an elongation of the jaws, which is presumably of advantage in feeding. The adaptive significance of advantage. However, it is difficult to ignore the most of the other osteological features that char- probable adaptive significance of photophores in acterize the various evolutionary groups (e.g., the lantemfishes, particularly in view of the fact that supramaxillary of the Gymnoscopelini) is only the next largest family of midwater fishes, the conjectural. Although most lanternfishes appear Gonostomatidae, is characterized by photophores to be filling the same general ecologic role, the placed in patterns that are often specifically dis- morphological specializations described above must tinct. While the details of the functional advantages be indicative of presumably important, but un- from different photophore patterns remain specu- known, differences in ecology. lative, the osteological evidence strongly indicates Photophore patterns have evolved in parallel that the photophore patterns of lantemfishes mirror with other morphologic characteristics. Some of the evolutionary history of the family. 78 BULLETIN OF THE NATURAL HISTORY MUSEUM OF LOS ANGELES COUNTY No.13

BONAPARTE, CHARLES L. J. L. 1840. Iconografia della fauna Italica per le quatro classi degli animali LITERATURE CITED vertebrati. Vol. 3, Pesci. Roma. (Not seen). BRAUER, AUGUST. 1904. Die Gattung Myctophum. Zool. Anzeiger 28 (10): 377-404. ALCOCK, ALFRED W. 1890. Natural history notes from H. M. Indian Marine Survey Steamer 'Investiga- 1906. Die Tiefsee-Fische. 1. Systematischer tor'. No. 16. On the bathybial fishes collected in Teil. Wiss. Erg. Deut. Tiefsee-Exped. "Valdivia" the Bay of Bengal during the season 1889-90. 1898-1899, 15 (1): 1-432. Ann. Mag. Nat. Hist., ser. 6, 6: 197-222. 1908. Die Tiefsee-Fische. 2. Anatomischer ANDRIASHEV, ANATOLE P. 1962. Bathypelagic fishes of Teil. Ibid. 15 (2): 1-266. the Antarctic. 1. Family Myctophidae. Akad. BUSSING, WILLIAM A. 1965. A study of the midwater Nauk S.S.S.R., Issled. Fauny Morei, 1 (9): 216- fishes of the Peru-Chile Trench. Amer. Geophys. 294. (Bur. Comm. Fish. Ichthyol. Lab. Transl. Union, Antarctic Res. Ser. 5: 185-227. 29). CLARKE, G. L., AND E. J. DENTON. 1962. Light and ANONYMOUS. 1961. International code of zoological animal life, Vol. 1, p. 446-468. In M. N. Hill (ed.) nomenclature adopted by the XV International The sea. Interscience Publishers, New York. Congress of Zoology. London. 176 p. CLARKE, WILLIAM D. 1963. Function of biolumines- BACKUS, R. H., J. E. CRADDOCK, R. L. HAEDRICH, D. L. cence in mesopelagic organisms. Nature 198 SHORES, J. M. TEAL, A. S. WING, G. W. MEAD, (4887): 1244-1246. AND W. D. CLARKE. 1968. Ceratoscopelus ma- COCCO, ANASTASIO. 1829. Su di alcuni pesci del Mari derensis: peculiar sound-scattering layer identified di Messina. Giorn. Sci., Lett., Arti Sicilia (Pa- with this myctophid fish. Science 160 (3831): lermo) 26: 138-147. (Not seen). 991-993. 1838. Su di alcuni Salmonidi del Mare di BARHAM, ERIC G. 1966. Deep scattering layer migra- Messina, lettera al Ch. D. Carlo Luciano Bona- tion and composition: observations from a diving parte. Nuovi. Ann. Sci. Nat. Bologna 2: 161-194. saucer. Science 151 (3716): 1399-1403. 1846. Giorn. Gabin. Lett. Messina, Ann. V. BECKER, V. E. 1963. New data on the lanternfish gen- 8: 63-64. (Not seen). era Electrona and Protomyctophum (Pisces, Myc- COLEMAN, LEONARD R., AND BASIL G. NAFPAKTITIS. tophidae) of the southern hemisphere. Vopr. Ikht. 1972. Dorsadena yaquinae, a new genus and 3, 1 (26): 15-28. (In Russian). species of myctophid fish from the eastern North 1964. Slendertailed myctophids (genera Low- Pacific Ocean. Nat. Hist. Mus. Los Angeles Co., eina, Tarletonbeania, Gonichthys and Centro- Contrib. Sci. 225: 1-11. branchus) of the Pacific and Indian Oceans. COSTA, ORONZIO G. 1855. Descrizione scientifica di un Systematics and distribution. Trudy Inst. Okean. nuovo pesce del Mediterraneo. Rendiconti Accad. 73: 11-75. (In Russian). Pontaniana, Napoli 1855: 11-14. BEEBE, WILLIAM. 1937. Preliminary list of Bermuda CRANE, JULES M. 1965. Bioluminescent courtship dis- deepsea fish. Zoologica (N.Y.) 22: 197-208. play in the teleost Porichthys notatus. Copeia , AND MARY VANDER PYL. 1944. Eastern Pacific 1965 (2): 239-241. Expeditions of the New York Zoological Society. CUVIER, GEORGES L.C.F.D. 1817. Le regne animal XXXII'. Pacific Myctophidae (fishes). Zoologica distribue d'apres son organisation. Vol. 2. Les (N.Y.) 29 (2): 59-95. reptiles, les poissons, les mollusques et les anne- BERG, LEO S. 1947. Classification of fishes, both recent lides. Paris. 532 p. and fossil. J. W. Edwards, Ann Arbor. 517 p. DAVID, LORE R. 1943. Miocene fishes of southern Cali- BERRY, FREDERICK H. 1964. Aspects of the develop- fornia. Geol. Soc. Amer. Spec. Pap. 43:1-193. ment of the upper jaw bones in teleosts. Copeia DEVEREUX, ROBERT F., AND ROBERT C. WINSETT. 1964 (2): 375-384. 1953. Isaacs-Kidd Midwater Trawl, final report. BOLIN, ROLF L. 1939. A review of the myctophid Oceanogr. Equip. Rept. 1, Scripps Inst. 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FRASER-BRUNNER, A. 1931. Some interesting West GREGORY, WILLIAM K. 1933. Fish skulls: a study of the African fishes, with descriptions of a new genus evolution of natural mechanisms. Trans. Amer. and two new species. Ann. Mag. Nat. Hist. Phil. Soc. 23 (2 ) : 75-481. (ser. 10) 8 (45) : 217-225. GREY, MARION. 1955. Notes on a collection of Bermuda 1949. A classification of the fishes of the deep-sea fishes. Fieldiana, Zool. 37: 265-302. family Myctophidae. Proc. Zool. Soc. London GUNTHER, ALBERT C.L.G. 1864. Catalogue of the 118 (4): 1019-1106. fishes of the British Museum, Vol 5. London. 455 p. FROST, G. ALLEN. 1926. A comparative study of the 1873. Zweiter ichthyologischer Beitrag nach otoliths of the neopterygian fishes (continued). Exemplaren aus dem Museum Godeffroy. J. Mus. Orders Haplomi, Heteromi, Iniomi, Lyomeri, Godeffroy (Hamburg) 4: 89-92. Hypostomodies, Salmopercae, Synentognathi, Mi- crocyprini, Solenichthys. Ann. Mag. Nat. Hist. 1876. 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LAVENBERG, ROBERT J., AND JOHN E. FITCH. 1966. Ocean. Bull. Los Angeles Co. Mus. Nat. Hist., Sci. Annotated list of fishes collected by midwater 5: 1-79. trawl in the Gulf of California, March-April , AND JOHN R. PAXTON. 1968. Review of the 1964. Calif. Fish and Game 52 (2): 92-110. lanternfish genus Lam padena with a description LEUCKART, SIGISMUND. 1821. Einiges iiber die fischarti- of a new species. Los Angeles Co. Mus., Contrib. gen Amphibien. Isis (Oken) 1 (6): 260-265. (Not Sci. 138: 1-29. seen). NELSON, GARETH J. 1967. Gill arches of teleostean LOWE, RICHARD T. 1839. A supplement to a synopsis fishes of the family Clupeidae. Copeia 1967 (2) : of the fishes of Madeira. Proc. Zool. Soc. London 389-399. 7: 76-92. 1969. Gill arches and the phylogeny of fishes, LUTKEN, CHRISTIAN F. 1892. Spolia Atlantica. Scope- with notes on the classification of vertebrates. lini Museu Zooligici Hauniensis. Bidrag til Kund- Bull. Amer. Mus. Nat. 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Mus. 97 classification of the orders Iniomi and Xenober- (3211) : 81-90. yces. Occ. Pap. Bingham Oceanogr. Coll. 2: 1-45. MOSER, H. GEOFFREY, AND ELBERT H. AHLSTROM. 1970. Development of lantemfishes (family Myc- PATTERSON, C. 1964. A review of mesozoic acanthop- tophidae) in the California Current. Part I. Species terygian fishes, with special reference to those of with narrow-eyed larvae. Bull. Los Angeles Co. the English Chalk. Philos. Trans. Roy. Soc. Lon- Mus. Nat. Hist., Sci. 7: 1-145. don, ser. B, Biol. Sci. 247 (739): 213-482. NAFPAKTITIS, BASIL G. 1966. Two new fishes of the PAXTON, JOHN R. 1967a. A distributional analysis for myctophid genus Diaphus from the Atlantic Ocean. the lanternfishes (family Myctophidae) of the Bull. Mus. Comp. Zool., Harvard 133 (9): 401- San Pedro Basin, California. Copeia 1967 (2): 424. 422-440. 1968. Lanternfishes of the genera Lobianchia 1967b. Biological notes on southern Califor- and Diaphus in the North Atlantic. 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PERTSEVA-OSTROUMOVA, T. A. 1967. Larvae of the STARKS, EDWIN C. 1901. Synonymy of the fish skeleton. primitive myctophids Protomyctophum and Elec- Proc. Wash. Acad. Sci. 3: 507-539. trona (Myctophidae, Pisces). Trudy Inst. Okean. 1916. The sesamoid articular, a bone in the 84: 222-237. (In Russian). mandible of fishes. Stanford Univ. Publ., Univ. PHILLIPS, JULIUS B. 1942. Osteology of the sardine Ser. 1916: 1-40. (Sardinops caerulea). J. Morphol. 70 (3): 463- STECHE, OTTO. 1909. Die Leuchtorgane Anoma- 500. von lops katoptron und Photoblepharon palpebratus, RAFINESQUE, CONSTANTINE S. 1810. Indice d'ittiologia zwei Oberflachenfischen aus dem malaiischen Siciliana. Giovanni del Nobol, Messina. 70 p. Archipel. Zeit. Wiss. Zool. 93: 349-408. RAY, D. L. 1950. The peripheral nervous system of SUPINO, FELICE. 1901. Ricerche sul cranio dei Teleostei. Lampanyctus leucopsarus. J. Morphol. 87 (1): I. Scopelus, Chauliodus, Argyropelecus. Ricerche 61-178. Lab. Anat. Norm., Roma 8: 249-273. REGAN, C. TATE. 1910. The caudal fin of the Elopidae TAANING, A. VEDEL. 1918. Mediterranean Scopelidae and of some other teleostean fishes. Ann. Mag. (Saurus, Aulopus, Chlorophthalmus, and Mycto- Nat. Hist. ser. 8, 5 (48) : 354-358. phum). Rept. Danish Ocean. Exped. 1908-10,2, A 1911. The anatomy and classification of the (7): 1-154. teleostean fishes of the order Iniomi. Ibid. ser. 8, 1928. 7 (37): 120-133. Synopsis of the scopelids in the North Atlantic. Vidensk. Medd. naturh. Foren. 86: 49-69. REINHARDT, JOHANNES C. H. 1837. Ichtyologiske bidrag til den Gronlandske fauna. Dansk Vid. Selsk. Afh. TAYLOR, W. RALPH. 1967. An enzyme method of clear- Kjobenhavn 1837, 6: 107-111. (Not seen). ing and staining small vertebrates. Proc. U.S. Nat. Mus. 122 (3596) : 1-17. RENSCH, BERNHART. 1959. Evolution above the species level. Methuen and Co., London. 419 p. WARBURTON, FREDERICK E. 1967. The purposes of RICHARDSON, JOHN. 1844. Ichthyology of the voyage of classifications. Syst. Zool. 16 (3): 241-245. H.M.S. Erebus and Terror, under the command of WEBER, MAX. 1902. Introduction et description de Captain Sir James Clark Ross, R.N., F.R.S. Zool. l'expedition. Siboga-Expedite, Monogr. 1: 1-159. 2: 1-139. Voyage Erebus and Terror 1913. Die Fische der Siboga Expedition. Ibid. RIDEWOOD, W. G. 1904. On the cranial osteology of 57: 1-710. the fishes of the families Elopidae and Albulidae, with remarks on the morphology of the skull in WErrzmAN, STANLEY H. 1962. The osteology of Brycon the lower teleostean fishes generally. Proc. Zool. meeki, a generalized characid fish, with an osteo- Soc. London 1904 (2): 35-81. logical definition of the family. Stan. Ichthyol. Risso, ANTOINE. 1810. Ichthyologie de Nice, ou his- Bull. 8 ( I ) : 1-177. toire naturelle des poissons du Department des 1967a. The origin of the stomiatoid fishes Alpes Maritimes. Paris. 388 p. with comments on the classification of salmoni- 1826. Histoire naturelle des principales pro- form fishes. Copeia 1967 (3) : 507-540. ductions de l'Europe meridionale et particuliere- 1967b. The osteology and relationships of the ment de celles des environs de Nice et des Alpes Astronesthidae, a family of oceanic fishes. Dana Maritimes. F. G. Levrault, Paris. Vol. 3: 1-480. Rept. 71:1-54. ROMER, ALFRED S. 1966. Vertebrate paleontology, WHITLEY, GILBERT P. 1933. Studies in ichthyology. ed. 3. Univ. Chicago Press, Chicago. 468 p. No. 7. Rec. Austral. Mus. 19: 60-112. ROSEN, DONN E. 1964. The relationships and taxo- nomic position of the halfbeaks, killifishes, silver- 1939. Studies in ichthyology. No. 12. Ibid 20 sides, and their relatives. Bull. Amer. Mus. Nat. (4): 264-277. Hist. 127 (5): 217-268. 1953. Studies in ichthyology. No. 16. Ibid 23 , AND COLIN PATTERSON. 1969. The structure (3): 133-138. and relationships of the paracanthopterygian 1968. A check-list of the fishes recorded from fishes. Bull. Amer. Mus. Nat. Hist. 141 (3): 357- the New Zealand region. Austral. Zool. 15 (1): 474. 1-102. SIMPSON, GEORGE G. 1949. The meaning of evolution. WISNER, ROBERT L. 1963a. Lampanyctus hubbsi, a new Yale Univ. Press, New Haven. 364 p. myctophid fish from the east-central tropical Pa- SMITH, C. LAVETT, AND REEVE M. BAILEY. 1962. The cific Ocean, with notes on the related, sympatric subocular shelf of fishes. J. Morphol. 110 (1): eastern Pacific species. Copeia 1963 (1): 16-23. 1-17. 1963b. A new genus and species of myctophid SMITH, HOBART M. 1945. Calcified cartilage in reptiles. Herpetologica 3 (1): 31-32. fish from the south-central Pacific Ocean, with notes on related genera and the designation of a SMITH, JAMES L. B. 1933. An interesting new mycto- new tribe, Electronini. Ibid. 1963 (1): 24-28. phid fish from South Africa. Trans. Roy. Soc. So. Africa 21 (2): 125-127. 30, 1970 1949. The sea fishes of South Africa. Central Received June News Agency, Ltd., Cape Town. 550 p. Accepted for publication March 27, 1972