Homology of Intermuscular Bones in Acanthomorph Fishes

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3241, 25 pp., 10 ®gures, 1 table Month 00, 1998

SVEN GEMBALLA1 AND RALF BRITZ2

ABSTRACT Myosepta of selected representatives of the fol- Patterson and Johnson's (1995) hypothesis that lowing acanthomorph taxa were investigated: Po- the single bony series of intermusculars in higher lymixiiformes, Lampridiformes, Paracanthoptery- acanthomorphs is the homolog of epineurals of gii, Beryciformes, Atherinomorpha, and Perco- lower teleosts is tested. Our results contradict morpha. A new technique, microdissection of al- their hypothesis at essential points because we cohol-stored specimens and polarized-light discovered epineural tendons in the normal epax- microscopy, was applied to study the three-di- ial position in different acanthomorphs that were mensional architecture of connective tissue ®bers considered to lack these. We conclude that the in epaxial parts of myosepta. Several invariable ®rst intermuscular bone of Polymixia is an epi- similarities were present in all taxa: an epineural central, the single series of intermuscular bones series of tendons or bones and a tendinous series of Holacanthopterygii are epicentrals, and the of lateral bands in the epaxial part of the myosep- neoneurals of some percomorphs are normal epi- tum, and an epicentral series of tendons or bones neurals. Phylogenetic implications of our results in the horizontal septum. are discussed.

INTRODUCTION Since Owen's initial studies (1846, 1866), known as myorhabdoi (Chapman, 1944). Re- three series of intermuscular bones of teleosts cently, Johnson and Patterson (1993) and have been known as epineurals, epicentrals, Patterson and Johnson (1995) studied inter- and epipleurals. In some teleosts two addi- muscular bones among major teleostean tional bony series are developed and are groups. One important result of their exten-

1 Lehrstuhl Spezielle Zoologie, UniversitaÈt TuÈbingen, D±72076 TuÈbingen, Germany. 2 Postdoctoral Fellow and Research Associate, Department of Herpetology and Ichthyology, American Museum of Natural History. Present address: Lehrstuhl Spezielle Zoologie, UniversitaÈt TuÈbingen, D±72076 TuÈbingen, Germany.

Copyright ᭧ American Museum of Natural History 1998 ISSN 0003-0082 / Price $0.00 2 AMERICAN MUSEUM NOVITATES NO. 3241 sive investigation is that the bony intermus- forces during locomotion (Nursall, 1956, culars are usually continued by ®ber bundles Willemse, 1972, Wainwright, 1983, Westneat of connective tissue in the same series as the et al., 1993). Collagenous ®ber bundles as bones. They extended the terms epineural, components of myosepta were not described epicentral, and epipleural to include these in- in detail or well understood until recently termuscular ®ber bundles that they named in- (Gemballa, 1995). Descriptions for the di- termuscular ligaments. They concluded that verse group of acanthomorph ®shes are still the single bony series found in higher acan- lacking and some are presented here for the thomorphs is not composed of epipleurals as ®rst time. The functional signi®cance of the generally assumed, but is the homolog of the results presented here is the topic of a forth- epineural series of lower teleosts that is shift- coming paper. ed ventrally into the horizontal septum. They conceded that ``recording details of ACKNOWLEDGMENTS the form and distribution of those structures [i.e., intermuscular bones and ®ber bundles] We thank Karsten Hartel (MCZ, Harvard), in cleared and stained specimens can be ex- and Norma Feinberg, Barbara Brown, Me- tremely dif®cult . . .'' (1995: 1) and that ``ob- lanie Stiassny, and Gareth Nelson (AMNH, servations of ligaments . . . include an un- New York) for the loan of study material. We known quantity of subjectivity, and we will express deepest gratitude to Dave Johnson be glad to see all or any of them checked by and Colin Patterson for providing a copy of others'' (1995: 4). their interesting and stimulating paper on te- Doubts concerning their homology of leost intermusculars before publication. Their acanthomorph intermusculars with epineurals enormous survey facilitated our work and arose during the doctoral study of Gemballa was the basis for constant checking of our (1995). He developed a technique to study data. We enjoyed discussion with Dave John- individual myosepta and reliably identify in- son during a short visit to the Division of termuscular ®ber bundles by polarized light. Fishes, National Museum of Natural History, This new technique revealed epineural ®ber Washington. We thank Gareth Nelson and bundles in taxa declared to lack them by Pat- Radford Arindell for inviting RB to join terson and Johnson (1995). Thus, it appeared them for ®eldwork in Alabama and for their to us that their applied technique misled Pat- interest in our ``intermuscular problem''. We terson and Johnson into homologizing the are grateful to Bob Shipp and the numerous single series of intermuscular bones in acan- individuals who helped in many ways during thomorphs with the epineural series of lower the 64th Annual Deep Sea Fishing Rodeo, teleosts. 1996, on Dauphin Island, Alabama. Eduard The aim of our paper is to reinvestigate Serrat and ®shermen from PalamoÂs (Catal- myoseptal structures of representatives of unya, Spain) made ®shing boat trips possible major acanthomorph subgroups using Gem- for SG. We thank Wolfgang Maier, Lehrstuhl balla's technique (1995) to test Patterson and fuÈr Spezielle Zoologie, UniversitaÈt TuÈbingen, Johnson's hypothesis. Anatomical data ob- for his interest in our project, and Melanie tained by this technique form the basis for Stiassny for her support. Barbara Brown, unequivocal identi®cation of the bony series Radford Arindell, and Martina Hohloch pro- in acanthomorphs as the homolog either of vided technical assistance. The paper pro®ted the epineural or the epicentral series of lower from the critical reading and commenting by teleosts. This is valuable because these struc- Peter Bartsch, Gareth Nelson, and Marcelo tures are incorporated in phylogenetic hy- SaÂnchez-Villagra and the reviews of An- potheses (Johnson and Patterson, 1993) that thony Gill (BMNH, London) and Mark W. are weakened or strengthened depending on Westneat (FMNH, Chicago). MWW drew the homologization (see Discussion). our attention to the terminology problems A detailed anatomical description of myo- with tendons and ligaments. septal structures is also of interest to func- This work was supported by the SFB 230 tional morphologists because these structures and a collection study grant from the Amer- are involved in transmission of muscular ican Museum of Natural History to SG, a 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 3

TABLE 1 Investigated Specimensa

Specimen SL(mm) Family Polymixia lowei AMNH 49674 103 POLYMIXIIDAE (c&s) Polymixia lowei AMNH 086102 97 POLYMIXIIDAE (c&s) Velifer hypselopterus AMNH 49575 115 VELIFERIDAE (c&s) Metavelifer multiradiatus AMNH 92080 ϳ279 VELIFERIDAE (skel.) Lampris guttatus AMNH 79669 ϳ820 LAMPRIDAE (skel.) Aphredoderus sayanus AMNH 55089 74 APHREDODERIDAE (c&s) Molva dipterygia personal coll. 220 GADIDAE (c&s, part) Gephyroberyx philippinus AMNH 49701 85 TRACHICHTHYIDAE (c&s) Hoplostethus mediterraneus personal coll. 106 TRACHICHTHYIDAE (c&s) Holocentrus rufus AMNH 25919 124 HOLOCENTRIDAE (c&s) Holocentrinae indet. MCZ 85252 11 HOLOCENTRIDAE (c&s) Holocentrinae indet. MCZ 85252 11.5 HOLOCENTRIDAE (c&s) Holocentrinae indet. MCZ 85252 13.5 HOLOCENTRIDAE (c&s) Holocentrinae indet. MCZ 51911 18 HOLOCENTRIDAE (c&s) Holocentrinae indet. MCZ 51911 26 HOLOCENTRIDAE (c&s) Bedotia geayi personal coll. 98 BEDOTIIDAE (c&s) Scomberesox saurus personal coll. 240 SCOMBERESOCIDAE (c&s) Channa obscura personal coll. 121 CHANNIDAE (c&s) Channa obscura personal coll. 126 CHANNIDAE (c&s) Anthias pleurotaenia AMNH 38119 100 SERRRANIDAE (c&s) Serranus hepatus personal coll. 72 SERRANIDAE (c&s) Lates calcarifer AMNH 37836 80 CENTROPOMIDAEb (c&s) Centropomus robalito AMNH 32925 99 CENTROPOMIDAE (c&s) Morone americana AMNH 57453 112 MORONIDAE (c&s) Percopsis omiscomaycus AMNH 27265 86 PERCOPSIDAE (c&s) Oligoplites saurus AMNH 45080 132 CARANGIDAE (c&s) Parupeneus barberinoides AMNH 43106 61 MULLIDAE (c&s) Kuhlia rupestris AMNH 17954 96 KUHLIIDAE (c&s) Arnoglossus laterna personal coll. 53 BOTHIDAE (c&s) ac&s ϭ cleared and double stained, skel ϭ skeletonized specimens, SL ϭ standard length. b Mooi and Gill (1995) gave full familial status to the centropomid Latinae. dissertational grant to RB from the Landes- much easier to identify in ethanol. A retrans- graduiertenfoÈrderung Baden-WuÈrttemberg fer into glycerin is possible whenever nec- and subsequently a postdoctoral fellowship essary. After a close examination, individual in the Department of Herpetology and Ich- myosepta were removed with ®ne iris spring thyology, American Museum of Natural His- scissors by cutting close to their insertion on tory, New York. the axial skeleton. Removed myosepta were mounted on slides, and studied under a MATERIAL AND METHODS stereomicroscope in transmitted light and un- Most specimens (see table 1) were cleared der a light microscope using transmitted light and double-stained according to the proce- or difference-interference contrast. Storage dure of Dingerkus and Uhler (1977). A few of individual myosepta was in 100% ethanol. data were gathered from large, skeletonized Polarized light microscopy has an advan- specimens. Length is given as standard tage in visualizing ®ber pathways within a length in millimeters. myoseptum, because of double-refraction of Glycerin-stored cleared and stained speci- collagen ®bers. Collagen ®bers are observed mens were transferred to 100% or 70% etha- as bright strands against a black background. nol because connective tissue elements are We photographed myosepta with a polarized 4 AMERICAN MUSEUM NOVITATES NO. 3241 light microscope (ZEISS Axioplan with cam- ments connect bone to bone. Therefore we era MC-100). Several photographs were use the term ``intermuscular tendons'' in- taken to cover the epaxial part of a myosep- stead of Patterson and Johnson's ``intermus- tum. Prints were later mounted on black cular ligaments.'' Accordingly, individual ®- cardboard to show the complete epaxial ber bundles are named epineural tendons, ep- myoseptum. icentral tendons (ϭ anterior oblique ten- Polarized light has some disadvantages. dons), epipleural tendons, and posterior Thick intermuscular bones are not translu- oblique tendons. cent, appear black, and thus are dif®cult to We maintain that ®ber bundles ®t the def- recognize. Thin intermuscular bones may be inition of tendon, not ligament, e.g., epineu- hard to distinguish from tendons in the pho- ral tendons connect epaxial musculature to tographs. However, ossi®cations were easy to the axial skeleton. Intermuscular tendons identify by their red Alizarin stain during dis- transfer muscular forces from myomeres to section. There are problems when collagen the axial skeleton and thus act as tendons. ®bers at angles of about 45 or 135Њ cross, When parts of the tendons ossify, the result- because of double refraction of collagen. One ing intermuscular bones may sometimes be of the two directions then appears almost connected to the axial skeleton via a short black and may seem to be lost in these cross- bundle of ®bers. Patterson and Johnson ing areas. Closer differential interference (1995) stressed that in such case the exact contrast (DIC) examination revealed this to term for this proximal part is ligament be- be an artifact and ®ber directions were al- cause then it connects bone to bone, i.e., in- ways continuous. Nevertheless, it was some- termuscular bone to axial skeleton. Ontoge- times dif®cult to ®nd an orientation that re- netically, however, it is the proximal portion vealed all ®ber directions to the same extent. of a tendon and we see no necessity to apply Individual myosepta of the following a different term to the same structure at a freshly caught species supplement the list in later point in ontogeny. table 1: Caranx hippos (Carangidae) and Sphyraena barracuda (Sphyraenidae). Myo- NUMBERING SEGMENTALLY ARRANGED septa were removed from adult specimens of STRUCTURES the two species during the 64th Annual Al- abama Deep Sea Fishing Rodeo on Dauphin The area of attachment of one myoseptum Island, July 19±21, 1996. First, the muscle encompasses several vertebrae and thus num- tissue was scooped out with a spoon. Then bering a myoseptum is problematic. For con- individual myosepta were cut close to the ax- venience, we number a given myoseptum ac- ial skeleton and preserved in 4% formalin. cording to the most anterior vertebra attached Remnants of muscle tissue were digested in to the anterior cone of the myoseptum. In all a trypsin solution and the myosepta rinsed in investigated specimens this is the same ver- water and photographed with incident light tebra attached to the epineural bone or epi- in front of a blackboard. neural tendon.

ABBREVIATIONS TERMINOLOGY BL Baudelot's ligament Distinct bundles of connective tissue ®bers DAC dorsal anterior cone occur in epaxial and hypaxial parts of myo- DPC dorsal posterior cone septa and in the horizontal septum. Patterson ecb epicentral bone and Johnson (1995) applied different terms ect epicentral tendon to these ®ber bundles naming them epineural, enb epineural bone epipleural and epicentral ligaments and pos- ent epineural tendon EFP epaxial ¯anking part terior oblique tendons (POTs). Westneat (per- ESP epaxial sloping part sonal commun.) pointed out to us the fact HFP hypaxial ¯anking part that the proper anatomical term for these ®- HSP hypaxial sloping part ber bundles is tendon and not ligament. Ten- lb lateral band dons connect muscle to bone, whereas liga- SH horizontal septum 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 5

VAC ventral anterior cone CONNECTIVE TISSUE FIBERS VPC ventral posterior cone IN EPAXIAL MYOSEPTUM When the epaxial part of the myoseptum RESULTS between the horizontal septum and the dorsal THREE-DIMENSIONAL SHAPE OF MYOSEPTUM posterior cone is removed and spread out, usually two ®ber bundles are recognized. Patterson and Johnson (1995) pointed out They are illustrated schematically in ®gure that intermuscular bones ossifying in the 1B and are shown for several species in sub- myoseptum are associated with strands of sequent ®gures. One bundle of ®bers origi- strong ®bers of connective tissue, their ``in- nates on the neural arch of the vertebra, fre- termuscular ligaments.'' These ®ber bundles quently as a distinct tendon, and extends pos- of connective tissue that we call intermus- terolaterally toward the integument, where it cular tendons (see above), are only parts of fans out distally. This bundle is the epineural the complete myoseptum. ligament of Patterson and Johnson (1995) Our description of a typical myoseptum and is here referred to as epineural tendon from the midbody region is based on ®ndings (see paragraph on terminology above). The of Gemballa (1995) and on additional data second bundle originates at the dorsal ante- from our study. Gemballa investigated rep- rior cone and also runs posterolaterally but resentatives of all major actinopterygian sub- then curves dorsally and fans out into the groups and found several invariable similar- dorsal posterior cone. We call this structure ities in the basic architecture of the myosep- the lateral band because it never shows the tum, i.e., the three dimensional shape and ar- characteristic convergence of ®bers that appear as a distinct tendon. It is more or less rangement of connective tissue ®bers. We prominent and resembles an aponeurosis in have con®rmed his results. Terminology for some species. Such a structure was not re- the different parts of the myoseptum is partly ported by Patterson and Johnson (1995) for adopted and modi®ed from Alexander any teleost that they studied. (1969), Willemse (1972) and Westneat et al. Ossi®cations can be found in both of the (1993). two ®ber bundles or only in one of them. The myoseptum is attached to the axial Ossi®cation in both ®ber bundles results in a skeleton medially. Its area of attachment ex- characteristic Y-shaped bone with proximal tends over several vertebrae, commonly forking. The anteromedial branch of the bone three, sometimes up to ®ve. The lateral area is embedded in the epineural tendon. This of attachment is the integument. When su- bone is attached either directly or via the perimposed in lateral view (®g. 1A), both ar- proximal part of the epineural tendon to the eas of attachment have the shape of (Ͼ ).The respective vertebra. The anterolateral branch myoseptum extends between the two areas of of the bone is embedded in the anterior part attachment. It is separated by the horizontal of the lateral band and ends free in the dorsal septum into epaxial and hypaxial parts. Both anterior cone. Ossi®cation in only one ®ber epaxial and hypaxial parts of the anterior bundle causes the regular slightly curved myoseptum point into dorsal and ventral an- splint of bone. Both types of ossi®cations are terior cones (DAC and VAC) close to the referred to as epineural bones by Patterson horizontal septum (SH). The posterior tips of and Johnson (1995). the (Ͼ ) point into dorsal and ventral posterior cones (DPC and VPC). The relative size of CONNECTIVE TISSUE FIBER BUNDLES anterior and posterior cones varies along the IN HORIZONTAL SEPTUM body and among taxa. Between anterior and The horizontal septum separates hypaxial posterior cones are epaxial or hypaxial slop- and epaxial parts of the myosepta and myo- ing parts (ESP or HSP). From the posterior meres. Two distinct ®ber bundles with dif- cones the myoseptum ¯exes anteriorly in the ferent orientations may be developed in the epaxial and hypaxial regions and forms epax- horizontal septum. They were called anterior ial and hypaxial ¯anking parts (EFP or HFP). oblique tendons (AOTs) and posterior 6 AMERICAN MUSEUM NOVITATES NO. 3241

Fig. 1. A, Schematic representation of typical myoseptum from midbody in lateral view, anterior to the left. Position of cones in epaxial part (DAC, DPC) and hypaxial part (VAC, VPC) and epaxial and hypaxial ¯anking parts (EFP, HFP) are shown. Areas of attachment areϾ -shaped. Dashed line represents medial area of attachment at axial skeleton; solid line lateral, area of attachment at integument. Area between anterior and posterior cone is called epaxial sloping part (ESP) and hypaxial sloping part (HSP), respectively (after Gemballa, 1995). B, Schematic representation of ESP of midbody myoseptum of left side, anterodorsal view. Arrangement of epineural tendon (ent) and lateral band (lb) is shown. Arrow points to position of epicentral bone or tendon that runs in horizontal septum. Its proximal part covered by DAC. 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 7 oblique tendons (POTs) (Kafuku, 1950, as connective tissue ®bers in the epaxial part of cited in Patterson and Johnson, 1995). The myosepta of selected taxa. We describe a typ- AOTs were called epicentral ligaments by ical myoseptum from the midbody region of Patterson and Johnson (1995), here referred a given taxon and then record changes that to as epicentral tendons (see above). The os- occur in anterior myosepta. si®cations within these tendons are the epi- POLYMIXIIFORMES: Polymixia lowei. Patter- central bones. Epicentral bones or tendons son and Johnson (1995) described the inter- are oriented posterolaterally. They are musculars of Polymixia in detail. There are crossed by the POTs that are oriented antero- two series, partly bony and partly tendinous laterally. (epineurals and epipleurals), and one tendinous series of epicentrals. The ®rst intermus- CONNECTIVE TISSUE FIBERS cular bone of Polymixia is stronger than the IN HYPAXIAL MYOSEPTUM others, lies in the horizontal septum, and ar- The hypaxial part of the myoseptum is ba- ticulates in a groove on the neural arch of the sically a mirror image of the epaxial part. ®rst vertebra. This is not the case in the more anterior myo- Myoseptum 13 (®g. 2A) bears a short but septa, where the abdominal cavity occupies well-developed epicentral tendon in the hor- more space and restricts the hypaxial mus- izontal septum. The epineural tendon is stout culature to narrow strips lateral to the ribs. and its posterior part approaches the lateral Exactly as in the epaxial part, the hypaxial band. Individual ®bers diverge along its part of the myoseptum shows two prominent length from the epineural tendon and cross ®ber bundles. One bundle originates on the the lateral band. The lateral band is broad rib or the dorsal part of the hemal arch and without any condensations of ®bers to dis- runs posterolaterally to the integument. It tinct bundles. was called epipleural ligament by Patterson Rostrally, epineural tendon 13 is well in and Johnson (1995) but, for reasons given, is line with the epineural tendons or bones of termed epipleural tendon. The other bundle the more anterior myosepta. Both bones and originates more dorsally and extends like- tendons insert on the neural arch of the re- wise posterolaterally and ventrally into the spective vertebrae. Epicentral tendon 13 is ventral posterior cone. There it ¯exes into the likewise in line with epicentrals of anterior hypaxial ¯anking part. We call this the lateral segments up to 2. In the ®rst myoseptum we band of the hypaxial myoseptum. Ossi®ca- ®nd a different situation (®g. 2B, C). When tions can be developed in both bundles re- observed in alcohol under the stereomicro- sulting in a proximally forked bone, or only scope, or with polarized light under the mi- in one bundle resulting in a slightly curved croscope, a distinct tendinous structure is unforked bone. Both types are referred to as present in the epineural position of myosep- epipleural bones by Patterson and Johnson tum 1. It is in line with epineurals of all sub- (1995). sequent vertebrae (®g. 2C). We therefore consider this tendon to be the epineural of FIBER BUNDLES IN FLANKING PARTS myoseptum 1. It inserts dorsal to the inter- (EFP, HFP) muscular bone of the ®rst vertebra. The in- There are no distinct tendons in either the termuscular bone is in the epicentral position epaxial or the hypaxial ¯anking parts of the in the horizontal septum and is in line with myoseptum. The ®bers commonly run lon- epicentral tendons of posterior segments. We gitudinally forming broad bands. These consider this to be the bony epicentral of bands may partly ossify in some teleosts and myoseptum 1 (see below). the resulting bones are called myorhabdoi af- LAMPRIDIFORMES: Velifer hypselopterus. ter Chapman (1944). Velifer is a deep-bodied ®sh and, as is fre- quently the case in myosepta of such ®shes, INTERMUSCULAR BONES AND TENDONS IN anterior cones are not developed. We show ACANTHOMORPHS myoseptum 11 (®g. 3A) of the midbody re- In the following paragraphs we present a gion. There is an epineural tendon with a detailed description of the arrangement of stout proximal end that inserts on the neural 8 AMERICAN MUSEUM NOVITATES NO. 3241

Fig. 2. Polymixia lowei. A, B. Micrographs of epaxial myosepta. Here and in all subsequent micrographs myosepta spread out: medial area of attachment to the left. A, Myoseptum 13. B, Myoseptum 1. C, Spatial relationship of epaxial myoseptum 1 and axial skeleton, lateral view, parts behind myoseptum illustrated in gray, modi®ed after Patterson and Johnson (1995). 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 9 spine and with a distal end that fans out. The mation in Velifer or Polymixia. Epineural broad lateral band coming from the DPC tendon of myoseptum 6 (®g. 4B) is not as crosses the epineural tendon and inserts distinct in its proximal part as that of 8. In along the height of the centrum. It appears addition, distance between the insertions of to be of equal thickness. In the horizontal epicentral and epineural has doubled com- septum there is an epicentral tendon that is pared to 8. This is caused by a dorsal shift crossed by three POTs. of the insertion of the epineural from the cen- In anterior myosepta some gradual trum in 8 to the neural arch in 6. In myosep- changes can be noticed. They are shown by tum 3 (®g. 4C) the epicentral tendon attaches photographs of myosepta 9, 4, and 1 (®g. to the ventral part of the centrum and the 3B±D). Epineural tendon 11 is aligned with distance between the insertions of epineural the series of epineural bones. The site of at- and epicentral tendons has increased further. tachment shifts from the neural spine in 9 to Epicentral tendons 8±3 are in line with epi- the neural arch in 1. Epineural bones 10±7 central bones in 2 and 1 (®g. 4D). Also epi- insert with a short proximal tendinous sheath neural tendons 1±8 are aligned and thus two and those of 6 to 1 articulate directly with complete series are present. vertebrae. We identi®ed epicentral tendons We observed a ventral shift of the epi- for myosepta 11±2 (see ®g. 3B, C for myo- neural and epicentral series toward the mid- septa 9 and 4) but failed to do so for myo- body region in our specimen of Hoplostethus septum 1. There it seems to be represented mediterraneus. The shift starts approximately by a diffuse bundle of ®bers at the level of at vertebra 6, which bears the ®rst hemal Baudelot's ligament (®g. 3D). spine. As the hemal spine lengthens in sub- Lampris guttatus. We were not able to sequent segments, the epicentral series shifts study myosepta of this lampridiform but further ventrally to the level of the distal end found differences from Patterson and John- of the hemal spines. Insertion of epineural son's (1995) account of its intermusculars. elements shifts ventrally from the neural arch The two anterior intermuscular bones of our to the centrum. Further caudally we recorded large specimen of L. guttatus (AMNH a dorsal shift of the two series. The epineural 79669) are attached to centra and not to neu- tendon is attached from vertebra 14 to the ral arches or spines. As already noted by Pat- neural arch. The insertion of the epicentral terson and Johnson, all following intermus- gradually shifts up to the centrum from ver- cular bones are attached to proximal portion tebra 16. of ribs. Gephyroberyx philippinus (not ®gured). BERYCIFORMES: Hoplostethus mediterra- The pattern of tendons and bones in Gephy- neus. Examination of myosepta 9±1 reveals roberyx is similar to that in Hoplostethus. the basic arrangement of the lateral band, There is ventral shift of the middle part of epineural, and epicentral tendons. Myosep- the whole series. The bony epicentrals of the tum8ofHoplostethus (®g. 4A) is thus sim- ®rst two myosepta attach to the neural arch, ilar to myosepta of the midbody region of followed by a series of epicentral tendons. Velifer (9, 11, ®g. 3A, B) or Polymixia (13, We failed to remove myoseptum 1 for a clos- ®g. 2A). It has a broad epicentral tendon in er examination but we were able to detect the horizontal septum. In this area of the epineural tendons dorsal to epicentrals in all trunk, vertebrae have long hemal spines. The remaining myosepta. There is also a lateral horizontal septum and epicentral tendons are band in the normal position in each myosep- displaced ventrally and attach at their distal tum. ends. Epineural tendon 8 inserts on the cen- Holocentrus rufus. Epineural 10 (®g. 5A) trum dorsal to the epicentral. Its ®bers di- is completely tendinous as in the posterior verge in its middle part and eventually fan segments. It inserts on the neural arch of ver- out at its distal end. The remaining part of tebra 10. There is an epicentral tendon in the the myoseptum consists of very ®ne, thin ®- horizontal septum. We found the same ar- bers that can be recognized only under po- rangement in myosepta 9, 8, and 7. In 8 (®g. larized light. Consequently, they form a very 5B) the epineural tendon bears a small ossi- faint lateral band when compared to the for- ®cation in its distal part, whereas the proxi- 10 AMERICAN MUSEUM NOVITATES NO. 3241

Fig. 3. Velifer hypselopterus. Micrographs of epaxial myosepta A, Myoseptum 11. B, Myoseptum 9. C, Myoseptum 4. D, Myoseptum 1. 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 11

Fig. 4. Hoplostethus mediterraneus. Micrographs of epaxial myosepta. A, Myoseptum 8. B, Myo- septum 6. C, Myoseptum 3. D, Myoseptum 1, epicentral bone broken twice. 12 AMERICAN MUSEUM NOVITATES NO. 3241 mal part remains tendinous. In 7 (®g. 5C) the termusculars of this species. Our specimen epineural bone is attached directly to the ax- had nine bony intermusculars in the horizon- ial skeleton. The site of insertion is shifted tal septum that represent the epicentral series. ventrally from the neural arch in 10, and the Bones 1 and 2 insert on the neural arch and centrum in 9, to the proximal part of the ven- posterior bones on the rib. This bony series tral rib in 8 and 7. The basic arrangement of is continued caudally by well-developed epi- ®bers in these myosepta of the midbody re- central tendons. Myoseptum 15 (®g. 6A) is gion is almost identical to that described for an example from the midbody region. There Polymixia (13, ®g. 2A), Velifer (9, 11; ®g. is a strong epicentral tendon with few POTs 3A, B), and Hoplostethus (8, ®g. 4A). attached to it, a lateral band of evenly dis- Anteriorly, each myoseptum from 6 to 3 tributed ®bers, and an epineural tendon with bears an epicentral tendon (see ®g. 5D±F). In converging ®bers. The myoseptum is thin, myosepta 2 and 1, epicentrals are ossi®ed. and the epineural tendon is visible only under We found some peculiar changes of the in- a microscope. termuscular bones in myosepta 6 (®g. 5D) to Molva dipterygia.AsinAphredoderus, 1, which we did not observe in other teleosts. there is a bony epicentral series in the hori- Starting with 6, a ventral shift of the epi- zontal septum. We show a myoseptum from neural bone can be noticed that involves the the midbody region (®g. 6B). It bears a small proximal part of the bone. This intermuscular epicentral ossi®cation in the horizontal sep- bone 6 is located in the lateral band but still tum that is embedded in a tendinous sheath attached to the rib as in 7. In myosepta 5, 4, and not attached to the axial skeleton. Well and 3 (marked by *, see ®g. 5E, F) the bones above the horizontal septum there is a broad have lost contact with the axial skeleton and epineural tendon with the ®bers converging are shifted further ventrally. They are in a slightly. They cross ®bers of an aponeurosis- position neither epineural nor epicentral but like, elongated lateral band. somewhat intermediate. There is still an ep- ATHERINOMORPHA: Bedotia geayi.Asre- icentral tendon beneath these bones. The corded by Patterson and Johnson (1995), strong epineural tendon of the midbody myo- there is a long series of bones in the hori- septa is not present here. Inserting at the cen- zontal septum of Bedotia. We show myosep- trum, there is a set of ®bers that resembles tum 15 (®g. 6C). There is a well-developed the epineural ®ber direction but the ®bers do bony epicentral in the horizontal septum with not extend to the integument. Bones of my- POTs crossing it. The lateral band is broad. osepta 2 and 1 (®g. 5G, H) are strongly de- The epineural is present but inconspicuous. veloped in sharp contrast to those of 5, 4, Scomberesox saurus. All myosepta of this and 3. They attach to centrum 2 or to neural elongate species exhibit long DACs and arch 1. They are in the horizontal septum and DPCs which is re¯ected by the presence of therefore we consider them epicentrals. a very long lateral band. As in Bedotia there This positional difference of intermuscular is a long series of epicentrals in the horizon- bones 1 and 2 (epicentrals) from those of 3, tal septum. We show myoseptum 11 (®g. 6D) 4, and 5 and from posterior ones (epineurals of this species. A bony epicentral is present 6 on) is re¯ected also by an ontogenetic dif- and a conspicuous lateral band. The epineur- ference. In a series of ®ve specimens of un- al is a faint structure consisting only of few determined Holocentrinae ranging from 11 to strands of ®bers. 26 mm SL, we found that intermuscular PERCOMORPHA: Lates calcarifer.Asde- bones 1 and 2 are well ossi®ed in all speci- scribed by Patterson and Johnson (1995), La- mens and attach to the neural arch. However, tes has a short series of four intermuscular bones posterior to 2 are not developed until bones in the horizontal septum of the ®rst the 26 mm stage. At this length we found six four vertebra which we homologize with epi- additional ossi®cations (3±8), none of them centrals (see below). Bones 1 and 2 attach to reaching the vertebral column. neural arches and 3 and 4 to ribs. These PARACANTHOPTERYGII: Aphredoderus say- bones are continued by epicentral tendons anus. We found some differences from Pat- that are hard to recognize from 4 through 9. terson and Johnson's (1995) report of the in- In ®gure 6E the weak tendon of 8 is shown. 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 13

Fig 5. Holocentrus rufus. Micrographs of epaxial myosepta. A, Myoseptum 10. B, Myoseptum 8. C, Myoseptum 7. D, Myoseptum 6. E, Myoseptum 5. F, Myoseptum 4. G, Myoseptum 2. H, Myoseptum 1. Note bony element (distal end marked by asterisk) shifting ventrally from margin of lateral band in D to area between epicentral tendon and lateral band in F (see discussion). Proximal ends of epineural tendons in D±H marked by arrowhead. 14 AMERICAN MUSEUM NOVITATES NO. 3241 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 15

More posteriorly, these tendons become above the epicentral. Myoseptum 1 (®g. 7F) more pronounced and were recorded by Pat- has the same arrangement as 2, but the epi- terson and Johnson (1995) for vertebra 12 neural tendon has a more diffuse appearance. and posterior segments. In addition to this Serranus hepatus and Pseudanthias pleu- epicentral series there is an epineural series rotaenia. We found 11 epicentral bones in dorsal to the former. In myoseptum 8, an ex- the horizontal septum in Serranus and 12 in ample for the midbody region, the epineural Pseudanthias. Figure 8A shows myoseptum tendon consists of numerous converging ®- 15 of Serranus. There is a distinct epineural bers. The lateral band is developed as the tendon with strongly converging ®bers. The normal broad band of evenly distributed ®- epicentral tendon is weakly developed. Both bers. This series of epineural tendons is con- epicentral and epineural series are continued tinued anteriorly as shown by myoseptum 2 anteriorly. In myosepta 8 (®g. 8B) and 2 (®g. (®g. 6F). Here the epineural tendon consists 8C), the epicentral is ossi®ed but there is no of fewer ®bers than the epineural tendon on remarkable change in the epineural tendon. vertebra 8. The epicentral bone is located be- The situation is very similar in Pseudanthias. low the epineural and crossed by few POTs. In both myosepta 8 (®g. 8D) and 3 (®g. 8E) Centropomus robalito. Centropomus has a the epineural tendon is well above the epi- pattern of intermuscular bones and tendons central bone. The lateral band is only weakly like that of Lates. Epicentral bones are re- developed. stricted to the anterior eight vertebrae with 1 Parupeneus barberinoides. Our specimen and 2 attached to neural arches and the sub- of Parupeneus bears a series of 14 epicentral sequent ones to ribs. Bony epicentrals are bones in the horizontal septum. Their site of continued by tendons that are weakly devel- attachment on the axial skeleton is the same oped. We show myoseptum 9 (®g. 7A) as an as reported for intermuscular bones (there example of this region. In contrast, epineural termed epineurals) of Upeneus by Patterson tendons are conspicuous and consist of nu- and Johnson (1995). In both genera this se- merous converging ®bers. They are accom- ries is continued by tendons. There is a sec- panied by a broad lateral band. Anteriorly, ond series of intermusculars above the hori- epineural tendons gradually change from dis- zontal septum, the epineural tendons,which tinct tendons to broad bands with ®bers con- can be traced rostrally to the second segment. verging only slightly. This can be noted in Kuhlia rupestris. Kuhlia has a series of myoseptum 3 in ®gure 7B. Below the epi- seven epicentral bones in the horizontal sep- neural tendon there is an epicentral bone. tum. As evidenced by myoseptum 5 (®g. Morone americana. Intermusculars of M. 9A), there is an epineural tendon above the americana strongly resemble those of Lates epicentral bone. It consists of several strong and Centropomus. The seven anterior myo- converging ®bers. Myoseptum 8 (®g. 9B) is septa have epicentral bones in the horizontal almost identical to 5 but the epicentral is ten- septum that are continued posteriorly by tendinous here. dons, as shown by myoseptum 11 (®g. 7C). Oligoplites saurus. The epicentral series of Epicentral and epineural tendons can be eas- Oligoplites consists of nine bony elements ily recognized. The lateral band is present. In continued caudally by tendons. We show my- myoseptum 6 (®g. 7D), the epicentral is bony osepta 10 from the midbody and 2 from the and the epineural tendon consists of fewer anterior region. Myoseptum 2 (®g. 9C) has a ®bers than that of 11. In myoseptum 2 (®g. bony epicentral. The lateral band is broad 7E), the epicentral bone is longer than in 6 and consists of thick ®bers. The epineural and attached to the neural arch. The epi- tendon is conspicuous and inserts on the neu- neural tendon is well-developed and inserts ral arch. Myoseptum 10 (®g. 9D) is different

← Fig. 6. Micrographs of epaxial myosepta. A, Aphredoderus sayanus, myoseptum 15. B, Molva dipterygia, myoseptum of midbody region. C, Bedotia geayi, myoseptum 15. D, Scomberesox saurus, myoseptum of midbody region. E, F. Lates calcarifer. E, Myoseptum 8. F, Myoseptum 2. 16 AMERICAN MUSEUM NOVITATES NO. 3241

Fig 7. Micrographs of epaxial myosepta. A, B. Centropomus robalito. A, Myoseptum 9. B, Myo- septum 3. C±F. Morone americana. C, Myoseptum 11. D, Myoseptum 6. E, Myoseptum 2. F, Myo- septum 1. 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 17

Fig 8. Micrographs of epaxial myosepta. A±C. Serranus hepatus. A, Myoseptum 15. B, Myoseptum 8. C, Myoseptum 2. D, E. Pseudanthias pleurotaenia. D, Myoseptum 8. E, Myoseptum 3. 18 AMERICAN MUSEUM NOVITATES NO. 3241

Fig 9. Micrographs of epaxial myosepta. A, B. Kuhlia rupestris. A, Myoseptum 5. B, Myoseptum 8. C, D. Oligoplites saurus. C, Myoseptum 2. D, Myoseptum 10. from 2 in that it is more elongate and has a ment of bones and tendons in the two myo- distinct DAC. The epicentral is tendinous septa is very similar. There is a strong epi- and has numerous POTs crossing it. The lat- central bone in both. The epineural tendon is eral band is a long and strong ®ber bundle. distinct at its proximal end and fans out to- The epineural tendon consists of several ward its distal part. The lateral band is dis- thick converging ®bers that attach to the neu- tinct and has the appearance of an aponeu- ral spine. rosis. Caranx hippos. We show myoseptum 2 Sphyraena barracuda. We show a myo- and one from the anterior abdominal region septum of the anterior body region of a large (precise segment unknown; ®g. 10A, B) re- adult (®g. 10C). There is an epicentral bone moved from an adult specimen. The arrange- with one POT attached to it. Similarly as in 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 19

Fig. 10. A±C. Photographs of epaxial myosepta. A, B. Caranx hippos. A, Myoseptum 2. B, Myo- septum from anterior body. C, Sphyraena barracuda, myoseptum from midbody. D±E. Channa obscura. D, Micrograph of horizontal septum from midbody, dorsal view, right side, anterior to the left. E, Micrograph of epaxial myoseptum 19. 20 AMERICAN MUSEUM NOVITATES NO. 3241

Caranx, the epineural tendon is distinct at its gated. One series is situated in the horizontal proximal end and fans out toward its distal septum, and the other dorsal to that in the part. The lateral band is a well-de®ned broad epaxial part of the myosepta. Thus we can band of dense ®bers. use the position as a simple criterion and ho- Channa obscura. This species bears a se- mologize the series in the horizontal septum ries of about 19 epicentral bones that is con- of acanthomorphs (anterior elements usually tinued posteriorly by a series of epicentral bony) with the epicentral series of lower tel- tendons. As shown by the micrograph of the eosts. The series (usually tendinous) in the horizontal septum (®g. 10D), the series is epaxial myosepta dorsal to the epicentral se- crossed by POTs. Above the series in the ries is homologized with the epineural series epaxial part of each myoseptum we again can of lower teleosts. demonstrate epineural tendon and lateral These homologies stand in contrast to the band (®g. 10E). Even if less pronounced, ®ndings of Patterson and Johnson (1995) they are present in all body segments. who hypothesized that the single bony series Arnoglossus laterna. This is the only per- in the horizontal septum is the epineural se- comorph we investigated bearing epineural ries that is shifted ventrally. In the subse- ossi®cations. There are Y-shaped epineural quent discussion we explain our line of evi- ossi®cations in the anterior 12 segments. In dence and discuss their hypothesis in light of subsequent myosepta only the lateral band our ®ndings. (but not the anteromedial branch) is ossi®ed. Thus the ossi®cations are C-shaped. Epicen- PATTERSON AND JOHNSON'S (1995) trals of the ®rst 12 segments are ossi®ed. HYPOTHESIS: VENTRAL SHIFT OF EPINEURALS DISCUSSION INTO HORIZONTAL SEPTUM Johnson and Patterson (1993) and Patter- Patterson and Johnson (1995) compared son and Johnson (1995) concluded that the the situation of intermusculars in Polymixia single bony series of intermusculars of most (considered the primitive euacanthomorph acanthomorphs is not the homolog of the epi- pattern), Holocentrus (primitive acantho- pleural series of non-acanthomorphs as was pterygian pattern), Lates (primitive perco- generally thought. We agree with this con- morph pattern), and Pseudanthias (derived clusion. Primitively, in acanthomorphs there percomorph pattern). Polymixia was hypoth- are three separate series of intermusculars, esized to show the most primitive state which in their unmodi®ed state are easy to among euacanthomorphs, because there are distinguish by their position: epineurals are three series of intermusculars: an epineural in the epaxial myoseptum, epicentrals in the series, predominantly bony, an epicentral se- horizontal septum, and epipleurals in the ries, completely tendinous, and an epipleural hypaxial myoseptum. However, that criterion series, partly bony and partly tendinous. does not work in most acanthomorph ®shes However, compared to what they take to be because there is only a single series of bones. primitive for acanthomorphs, Polymixia Even assuming that bony series may shift shows one derived feature: The ®rst inter- during phylogeny, as already noted by Owen muscular bone, which they homologized (1846, 1866), one problem of homology re- with the epineural of the ®rst vertebra, no mains: Is the single bony series in most acan- longer lies in the epaxial myoseptum but is thomorphs the homolog of the epicentral or shifted ventrally into the horizontal septum. of the epineural series of lower teleosts? In Holocentrus, considered by them to ex- In each series, a bone or a tendon corre- emplify the primitive state for acanthopter- sponds to a bone or a tendon in about the ygians, not only one but the ®rst ®ve to seven same position in the adjacent myosepta. intermuscular bones, which they consider (Only Holocentrus seems to be an exception, epineurals, are shifted ventrally into the hor- see discussion below.) We present evidence izontal septum. that there are two series, either tendinous or Eventually, in percomorphs all intermus- bony, in all acanthomorph species investi- cular bones, which they claim to be epineu- 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 21

rals, lie in the horizontal septum. Therefore, HOMOLOGY OF INTERMUSCULAR BONE ON they hypothesized that all epineurals are FIRST VERTEBRA IN POLYMIXIA shifted ventrally into the horizontal septum. Accordingly, this ventral displacement of the Patterson and Johnson (1995) identi®ed epineurals into the horizontal septum has the ®rst intermuscular bone of Polymixia as taken place in three steps, which Johnson and an epineural that is displaced ventrally from Patterson also used to de®ne monophyletic its position in the epaxial part of the myo- groups (see below). septum into the horizontal septum. They The ®rst step, ventral displacement of the based their homology on two lines of evi- ®rst epineural into horizontal septum (John- dence (1995: 33) : (1) the ®rst intermuscular son and Patterson, 1993: 601, character 8), is ``develops in series with the epineurals and considered a synapomorphy for their Eu- is fully formed at 12 mm SL, before the epi- acanthomorpha (Acanthomorpha minus centrals are recognizable'' and (2) ``there is Lampridiformes). The second step, ventral no lower teleost in which the epicentral se- shift of anterior epineurals into horizontal ries contains just one bone on V1 followed septum (ibid., p. 603, character 14), is con- by a series of ligaments''. sidered a synapomorphy for their Holacan- We have demonstrated above that a dis- thopterygii (Acanthomorpha minus Lampri- diformes and Polymixiiformes). The ®nal tinct tendinous structure originates dorsal to step, ventral displacement of all epineurals the origin of the ®rst intermuscular and is into horizontal septum (ibid.,p. 615, charac- aligned with the subsequent epineural bones ter 32), is considered a synapomorphy of (®g. 2). We therefore interpret this tendon as their Percomorpha (which includes Atheri- the epineural of the ®rst vertebra. It was not nomorpha). reported and apparently overlooked by them. They discovered, unexpectedly, a series of This may be caused by the different tech- tendinous structures above the epineural se- nique that they applied, i.e., studying speci- ries in a number of percomorph taxa. Ac- mens in glycerin. cording to their hypothesis, this dorsal series We think that an epineural tendon on the is not an epineural series because that series ®rst vertebra in Polymixia is suf®cient evi- is located in the horizontal septum. Conse- dence that the bone ventral to this tendon is quently, they concluded that the tendinous not a ventrally shifted epineural bone, and series above the epineurals is a neoforma- we want to address their argument brie¯y. tionÐthe so-called ``neoneural ligaments.'' The intermuscular bone on the ®rst vertebra These ``neoneural ligaments'' may even os- ``develops in series with the epineurals and sify in some bothid and samarid species and is fully formed at 12 mm SL, before the epi- then represent ``neoneural bones.'' centrals are recognizable'' (Patterson and Patterson and Johnson had doubts con- Johnson, 1995: 33). We consider this argu- cerning their method of recognizing tendons ment to be invalid because the identi®cation in glycerin-stored cleared-and-stained speci- of epicentral tendons in 12 mm long cleared- mens (1995: 4) : ``. . . we cannot pretend that and-stained specimens would be impossible observing and recording intermuscular liga- with their technique. The fact that ``there is ments is an entirely objective procedure. . .''. no lower teleost in which the epicentral se- On the other hand they also found that ``Transferring cleared-and-stained specimens ries contains just one bone on V1 followed to alcohol may render the ligaments more by a series of ligaments'' (1995: 33) is not opaque, and so more visible'' (1995: 4). evidence that this is impossible, but rather We used alcohol along with microdissec- that Polymixia is unique in this respect. tion, light- and DIC-microscopy, and polar- In summary there is strong and unambig- ized light to demonstrate the presence of var- uous evidence that the ®rst vertebra of Po- ious tendinous structures apparently over- lymixia has an epineural tendon. Therefore, looked by them. We consider our method the ®rst intermuscular bone of Polymixia is more objective, which leads to reproducible not an epineural, as claimed by Patterson and results. Johnson (1995), but an epicentral. 22 AMERICAN MUSEUM NOVITATES NO. 3241

INTERMUSCULAR BONES IN LAMPRIDIFORMES sion that Patterson and Johnson must have overlooked the epineural tendons. There is only a slight difference between our and Patterson and Johnson's (1995) INTERMUSCULAR BONES IN BERYCIFORMES specimen of Velifer. We could not identify the discrete epicentral tendon of the ®rst ver- We described a continuous tendinous se- tebra as described by them. Both investiga- ries in the epineural as well as in the epicen- tions reveal a tendinous epicentral series in tral position (bony on V1 and V2) for Ho- the horizontal septum. The series dorsal to plostethus and Gephyroberyx. These results that is tendinous in its posterior part and allow unequivocal homology. In Patterson bony in its anterior part. It is in an epineural and Johnson's (1995) Hoplostethus speci- position. We thus consider it an epineural se- men, they recorded only a series of epicentral ries. tendons from vertebra 9 backward and two Differences between our and their speci- bones on V1 and 2 in the epicentral position. men of Lampris guttatus in the attachment of They interpreted the two bones as epineural the ®rst two intermuscular bones are inter- bones shifted ventrally into the horizontal esting. We found both anterior bones at- septum. In light of our results, we think that tached to the centrum. The ®rst stout bone they overlooked the real epineural tendons in even articulates in a well-developed, deep the anterior 8 myosepta because they were groove of the centrum. All subsequent inter- unrecognizable in glycerin-stored cleared- muscular bones attach to the proximal parts and-stained specimens. of the ribs. This arrangement of intermus- Homologization of intermuscular bones in cular bones is characteristic for the epicentral our Holocentrus specimen is unambiguous bones of higher acanthomorphs (see discus- for myosepta from 7 backward. We found a sion below). In fact, they (Johnson and Pat- continuous series of tendons in the horizontal terson, 1993: 558) have already pointed out septum preceded by bones on V1 and V2, this resemblance but concluded that this and we regard these as homologs of epicen- placement is developed independently in tral tendons or bones. The series dorsal to the Lampris and higher acanthomorphs. It would epicentrals is the epineural series. In myo- be worth investigating myosepta of this spe- septa 6 to 1, these bony elements undergo a cies to check the precise placement of inter- remarkable ventral shift. In myosepta 4 and muscular bones in the myoseptum and to re- 3, they are situated even ventral to the lateral consider their possible homology with epi- band. It is not clear whether an epineural ten- centrals. don is present as well. We are not sure how to interpret this pattern of bones lying be- INTERMUSCULAR BONES IN tween the epineural and epicentral position. PARACANTHOPTERYGII Because we have not seen a similar arrangement in any other species, we are inclined to There are no dif®culties in homologizing interpret these as autapomorphic for Holo- intermusculars in Molva and Aphredoderus, centridae. because in both genera there is a bony/ten- For the two bony elements in the horizon- dinous epicentral series in the horizontal septal septum, the question arises whether they tum and a tendinous epineural series in the are true epicentrals, as claimed above, or epi- epaxial part of the myoseptum. Patterson and neurals that have shifted further ventrally as Johnson (1995) identi®ed a single bony se- claimed by Patterson and Johnson (1995), ries in the horizontal septum of the paracan- who investigated two species, Holocentrus thopterygians, Percopsis guttatus, Aphredo- spinifer and Holocentrus vexillaris. They derus sayanus, Raniceps raninus, and Gai- failed to recognize tendinous epicentrals 3 to dropsaurus mediterraneus, and homologized 8 but recorded them from 9 backward. They them with epineural bones shifted ventrally considered the two bones on V1 and V2 as into the horizontal septum. We did not rein- epineurals because the bones are in line with vestigate all species but our different ®ndings other epineural elements. We have demon- in Aphredoderus sayanus led to the conclu- strated that these bones on V1 and V2 are in 1998 GEMBALLA AND BRITZ: INTERMUSCULAR BONES IN ACANTHOMORPHS 23 line with the epicentral series. Patterson and the homology of Patterson and Johnson Johnson may have overlooked epicentral ten- (1995). They claimed that the single series of dons 3 to 8 because the tendons are dif®cult intermuscular bones in percomorphs is the to detect by examination of glycerin speci- epineural series that has shifted ventrally. mens but, according to our ®ndings, more This homology is based on a comparison of easily detected by dissection and microscopy. intermusculars of Polymixia, Holocentrus, Our interpretation that the ®rst two inter- and Centropomus. They considered the po- muscular bones are epicentrals and thus dif- sition of the intermusculars in these three fer from the posterior bones is further sup- taxa to be a morphocline re¯ecting ventral ported by ontogenetic differences that we displacement of epineurals into the horizon- found between the two bone groups. The ®rst tal septum during evolution. two intermuscular bones are already present However, we have seen that (1) the inter- in the smallest larva available (11 mm), muscular bone on V1 of Polymixia is not an whereas 3 to 6 ossify in line with true epi- epineural, (2) other beryciforms like Hoplo- neural bones of 7 backward, but not before stethus have epineural tendons dorsal to their the 26 mm stage. series of intermuscular bones, and (3) centro- pomids also possess a series of epineural ten- INTERMUSCULAR BONES IN ATHERINOMORPHA dons dorsal to their series of intermuscular bones. For these reasons we conclude that In none of the atherinomorphs (Bedotia Patterson and Johnson (1995) were misled in sp., Menidia peninsulae, and Exocoetus vol- homologizing the single series of intermus- itans) they investigated did Patterson and cular bones with epineurals of lower teleosts. Johnson (1995) record two intermuscular el- Our results present unambiguous evidence ements within a single myoseptum. With the that there are epineural tendons in Perco- exception of some posterior segments in Me- morpha and that their single bony series is nidia, they reported only a bony series in the actually the homolog of the epicentral series horizontal septum, which was interpreted as of lower teleosts. epineural shifted ventrally. Again, with our Patterson and Johnson (1995) reported technique, we detected two intermuscular el- tendons in the position of epineurals of lower ements in a single myoseptum for Bedotia teleosts also in a number of percomorph rep- geayi and Scomberesox saurus. We consider resentatives (Ammodytidae, Pomacentridae, the bony elements in the horizontal septum Polynemidae, Mullidae) that even ossify in to be epicentrals, and the tendinous elements the pleuronectiforms Samaris and Bothus situated above the horizontal septum to be (and Arnoglossus according to our observa- epineurals. tions). Because they claimed that epineurals of percomorphs are ventrally displaced and INTERMUSCULAR BONES IN PERCOMORPHA located in the horizontal septum, Patterson In all percomorphs there is only one series and Johnson concluded that the series of ten- of intermuscular bones, which has generally dons in the position of epineurals of lower been referred to as epipleural. Patterson and teleosts is something different. They there- Johnson (1995) pointed out that this series is fore called those tendons ``neoneurals'' and not the homolog of the epipleural series of reported them in additional percomorph taxa: lower teleosts, and we agree with this state- Teraponidae, Kuhliidae, Carangidae, Eche- ment. neidae, Lutjanidae, Caesionidae, Gerreidae, We have demonstrated above that there are Sparidae, Lethrinidae, Sciaenidae, Haemuli- tendons in the position of epineurals dorsal dae, Labridae, and Scaridae. to the intermuscular bones in all perco- In percomorphs, presence of tendinous morphs that we investigated. The tendons in- structures that occur in the position of epi- sert on the neural arches of the respective neurals of lower teleosts is additional evi- vertebra and we homologize them with epi- dence for our hypothesis that intermuscular neural tendons. Therefore, the intermuscular bones in percomorphs are epicentrals. We bone situated ventral to the tendons is not an have checked myosepta of some of these taxa epineural but an epicentral. This contradicts that are reported to possess ``neoneurals'' 24 AMERICAN MUSEUM NOVITATES NO. 3241

(see above Kuhlia, Parupeneus, Oligoplites, 20) used to support a group Zeiformes ϩ Eu- Caranx) and found the same basic pattern of acanthopterygii and ``Point of origin of all epineurals and epicentral bones in the myo- but the ®rst two epineurals displaced ven- septum that we reported for other perco- trally, and the distal parts of all epineurals morphs (see above). We therefore have no displaced ventrally into the horizontal sep- doubt that percomorph ``neoneurals'' are tum'' (1993: 615, character 32) used to sup- normal epineurals and that percomorph `èpi- port their Percomorpha (including Atherino- neurals'' are epicentrals. morpha). A series of epicentral bones may turn out PHYLOGENETIC IMPLICATIONS AND to be a synapomorphy for their Holacanthop- CONCLUDING REMARKS terygii. However, further studies are needed to support such a hypothesis. We have presented convincing evidence Our hypothesis explains several of their that (1) the ®rst intermuscular bone of Po- con¯icting data. lymixia is an epicentral and (2) the single se- 1. The ventral position of the intermus- ries of intermuscular bones in higher acan- cular bones of Paracanthopterygii, some Ste- thomorphs is the homolog of the epicentral phanoberyciformes, and Zeiformes need not series of non acanthomorphs. If this interpre- be explained as a downward shift of epi- tation is accepted then the synapomorphy neurals acquired independently from that in ``First epineural displaced ventrally into the Percomorpha (which include Atherinomor- horizontal septum'' used by Johnson and Pat- pha). Rather it is the plesiomorphic retention terson (1993: 601, character 8) to support of an epicentral bony series. their Euacanthomorpha (Acanthomorpha mi- 2. In zeiforms and percomorphs the ante- nus Lampridiformes) is invalid. We think rior POTs are thought (Patterson and John- that the phylogenetic position of Lampridi- son, 1995: ii) to `àcquire a new association, formes basal to Polymixiiformes needs crit- attaching to epineural bones secondarily po- ical reexamination especially in the light of sitioned in the horizontal septum.'' Our hy- the sister-group relationship of Polymixia and pothesis does not need such an assumption all remaining acanthomorphs proposed by because the bones in the horizontal septum other authors (Rosen, 1985; Stiassny, 1986; are epicentrals and thus the situation of POTs Patterson and Rosen, 1989; Stiassny and in zeiforms and percomorphs is a retention Moore, 1992). of the plesiomorphic association between the Accepting our hypothesis also invalidates two systems. the following characters as synapomorphies: 3. The concept of ``neoneurals'' in some `Èpicentral ligaments absent anteriorly'' percomorphs is super¯uous because the (Johnson and Patterson, 1993: 603, character ``neoneurals'' are true epineurals. 13) and ``Distal parts of anterior epineurals As Patterson and Johnson (1995) have displaced ventrally into horizontal septum'' stressed, intermusculars of teleosts hold (1993: 603, character 14) used by Johnson much potential for resolution of phylogenet- and Patterson to support their Holacanthop- ically problematic groups, and we hope that terygii. `Ànterior epineurals displaced ven- our improvement of their method will help trally on to the ribs'' (1993: 606, character in accomplishing this goal.

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