Lago, a NEW GENUS of CARCHARHINID SHARKS, WITH

lago, A NEW GENUS OF CARCHARHINID SHARKS, WITH

A REDESCRIPTION OF /. omanensis

Leonard J. V. Compagno' and Stewart Springer"

ABSTRACT

A new genus, lago, is proposed for Eugaleiis omanensis Norman, 1939. /. omanensis, originally described from a single specimen, is redescribed from 16 additional specimens from the northern Arabian Sea continental shelf and slope between the Gulf of Oman and the Gulf of Kutch. Its presence in areas of low oxygen and the possibility of its occurrence in deeper waters of the Red Sea are discussed.

Norman (1939) described Eugaleus omanensis ographic Institution, 1965). Sixteen specimens from a 280-mm female specimen, taken at 210-m of a small carcharhinid were included in these depth in the Gulf of Oman. He placed it in collections and sent to us through the Smith-

Eugaleus Gill, 1864 ( = Galeorhinus Blainville, sonian Oceanographic Sorting Center. They 1816) with reservations because omanensis dif- were tentatively identified by us as Galeorhinus fered from all other species of Eugaleus in den- omanensis (Norman). tition and absence of a pronounced ventral Marshall and Bourne (1964, 1967), in photo- caudal lobe. Norman noted that omanensis did graphic surveys of benthic fishes, collected 30 not fit Hemigaleus Bleeker, 1852 because of den- photographs of a small carcarhinoid shark tition differences and lack of precaudal pits but (about 2 ft long) at depths between 1115 and he declined to establish a new genus for it. 2195 m in the Red Sea. They noted that their Fowler (1941) overlooked Eugaleus omanen- shark might be either a triakid or a carcharhinid sis in his review of Indo-Pacific elasmobranchs but was not identifiable to genus or species. Com- but later (1956) gave a description of the species parison of Marshall and Bourne's photographs condensed from Norman's account and allocated and sketch of their "mystery shark" with our it to the genus Galeorhinus. Misra (1949) had specimens and Norman's account of G. omanen- earlier placed it in the same genus but this was sis led us to suspect that the "mystery shark" not mentioned by Fowler. might be omanensis. Smith (1957) revised Galeorhinus but also We then sent two specimens of the IIOE series overlooked G. o?nanensfs. Compagno (1970) re- to Dr. N. B. Marshall at the British Museum viewed the systematics of Hemitriakis, Galeo7'- ( Natural History) . At our request he compared hinus, and related genera. He considered G. them with the holotype, the hitherto only known omanensis generically distinct from Galeorhinus specimen of Galeorhirms omanensis, and con- but did not propose a new genus in deference firmed our identification of the IIOE specimens. to this paper. He also agreed that the IIOE omanensis are very During the International Indian Ocean Expe- similar to the Red Sea "mystery shark" of the dition (IIOE) in 1963, the RV Anton Bruun on photographs, but noted that final identification Cruise 4B conducted 109 trawling stations in of the Red Sea species must await capture of ti'ansects along the continental shelf of the Arab- specimens. ian Sea between Bombay and the Gulf of Oman Differences between "Galeorhinus" omanensis at depths from 15 to 375 m (Woods Hole Ocean- and members of Galeorhinus, Hypogaleus, Hem- itriakis, and all other carcharhinid genera war- ' Stanford University, Stanford, Calif. 94305. rant the erection of a new genus for "Galeor- " National Marine Fisheries National Center Service, hinus" omanensis. for Systematics, Washington, D.G. 20560.

Manuscript accepted February 1971. FISHERY BULLETIN: VOL, 69, NO. 615 FISHERY BULLETIN: VOL. 69, NO. 3

Figure 1.—lago omanensis, from a 565-mm female deposited in U.S. National Museum. Drawing by Mildred H. Carrington.

We follow Compagno in uniting, at least provis- ionally, the two families. lago thus falls into lago GENUS NOVUM the family Carcharhinidae (sensu lato). lago is far from the advanced and intermediate omanensis NORMAN, 1939, Eiigaleus carcharhinid discussed TYPE-SPECIES genera by Compagno (1970). These genera include Hemigaleus, Galeocerdo, Scoliodon, Rhizoprioiv- Etymology Hemipristis, odon, Loxodon, Negaprion, Triaenodon. Lamiop- This shark, a namesake of the villain of sis, Isogomphodon, Carcharhinus, Hypoprion, Shakespeare's Othello, is a troublemaker for and Aprionodon. lago differs from all of these systematists and hence a kind of villain. in having a transitional, not internal, nictitating lower eyelid with edge nearly horizontal; shal- Follows Diagnosis (Terminology Compagno, low subocular pouch; teeth with strong basal 1970) ledges and grooves; teeth at symphysis only lago (Figure 1) differs from most carchar- slightly smaller than adjacent ones; no precau- hinoids in the extremely anterior origin of its dal pits; pectoral fin skeleton projecting less than first dorsal fin. fin distal radials as Only Isogomphodon oxyrhyn- halfway into ; pectoral only chus, a few species of Carcharinus, and the long as proximals, with parallel edges and trun- sphyrnid Eusphyra blochii rival lago in this cate tips (not tapered and acute); caudal fin respect. without projecting ventral lobe and lateral un- lago is morphologically intermediate bet\veen dulations of its dorsal margin in adults; cran- the families Triakidae and Carcharhinidae as ium with a complete supraorbital crest (absent in defined by Bigelow and Schroeder (1948) and advanced forms); and a spiral, not scroll, in- Garrick and Schultz (1963). The characters testinal valve (Hemigalejis and Hemipristis are of lago strengthen the evidence presented by exceptional in also having spiral valves). Compagno (1970) against separation of these lago differs from Galeorhinns and HypogaJeus families on simple nictitating lower eyelid and as delimited by Compagno (1970) in having a dental characters advocated by these writers. transitional rather than internal nictitating low-

616 COMPAGNO and SPRINGER: NEW GEN'LS OF CARCHARHINID SHARKS

er eyelid in adults, with nearly horizontal edge; anterior nasal flap not greatly reduced; teeth without postlateral cusplets; an interdorsal ridge present; lateral trunk denticles much longer than wide in adults (about as long as wide and no ventral in Hypogaleus and Galeorhinus) ; lobe on caudals of adults. From the curious Le.pfocharias, logo differs in having a transitional rather than internal nictitating lower eyelid in adults; much larger spiracles; no nasal barbel; very weak gynandric heterodonty; teeth with primary cusps oblique, not erect, and lacking cusplets; sharp-edged, FiGURE 2,—lago omnnensis. A. Ventral side of head. bladelike cutting teeth; fewer total vertebrae, B. Dor.sal side of head. to to in 130 147 (198 214 Leptocharias) ; spiral ior teeth dorsal fin base mid- intestinal valve with about 5 turns (14 to 16 in (not comblike) ; crest point closer to pectoral base termination than Leptocharias) ; and an entire supraorbital (reduced in Leptocharias to isolated preorbital pelvic origins (vice-versa in Proscyllium and

Eridacnis) ; second dorsal origin anterior and postorbital processes) . (not over or to anal fin lago can be distinguished from Hemitriakis, posterior) origin; intermedialia of vertebral centra Furgaleus, Scylliogalens, the Triakis-Miistelns strong wedges (not in and complex, Proscyllium, and Eridac^us by its more wedgelike Proscyllium Eridacnis) ; large absent from arches and buccal cavi- lateral eyes, in dorsal view nearly touching head papillae gill and nostrils farther rim, and its sharp-edged, monocuspidate teeth. ty; apart. lago also lacks the In addition, lago differs from He>nitriakis in clasper hooks, scyliorhinoid color pattern, and the having a transitional rather than external nic- apparently oviparous reproduction of Pros- titating lower eyelid, noncarinate posterior teeth, cyllium. more tooth rows (only 18 to 36/29 to 34 in weak transverse notches on Hemitriakis) , teeth, GENERIC DESCRIPTION and no ventral caudal lobe. lago lacks the short, thick, rounded snout, nasoral grooves, and molar- Head flattened, its length from snout tip to iform teeth of and also has fewer fifth Scylliogalens gill opening about i/i. total length. tooth rows and series of teeth functional. Un- Eye openings dorso-lateral, not visible in like Furgaleus, lago lacks nasal barbels, erect ventral view of head, openings elongate, about cusps on its lower anterolateral teeth, and a twice as long as high, with a well-developed ventral caudal lobe; has also, lago (Figure 2) posterior notch ; nictitating lower eyelid trans- the nostrils definitely closer to the mouth than itional (Figure 3B), its edge nearly hoi'izontal;

the snout tip (about equidistant in Furgaleus) . secondary lower eyelid strongly differentiated, lago differs from most members of the Triakis- its edge thin; subocular jjouch shallow, its lateral Mustelus complex in having fewer tooth rows and surface bare of denticles. series of teeth functional; however, Triakis sem- Slitlike spiracles, length about J'- eye length, rivals in -- ifasciata lago these respects. lago does located about eye length behind and slightly not have a of pavement molariform teeth as in below posterior eye notch; external gill slits mod- Mustelus; also, its pelvic anterior margins are erately short, lengths in adults nearly equal, the less than half the of length pectoral anterior longest 1,4 to % eye length; nostrils located in margins (over half as long Triakis-Mustelus) . about one-half as far from mouth as from snout Finally lago contrasts with Proscyllium and tip, well separated, without nasoral grooves, Eridacnis by its transitional, not rudimentary, widths about 1% to 2 times internarial dis- nictitating lower eyelid; monocuspidate poster- tance, anterior nasal flap a short truncate lobe.

617 FISHERY BULLETIN: VOL, 69, NO. 3

Mouth opening subtriangular, broad, 2 to 214

times as wide as long ; labial furrows extending around mouth corners, the upper furrows longer, extending anteriorly only to below eye pupils; large papillae absent from buccal cavity. Teeth small (Figures 3A and 4), largest with Figure 4.—lago omanensis. Teeth of right side of upper at root 1.5 in greatest width about mm 457-mm and lower jaws; labial aspect. Dotted lines indicate female; tooth rows 46 to 55/37 to 45; 2 to 3 jaw symphysis. series functional along edges of jaws; teeth in mixed alternate and imbricate overlap pattern primary cusp and no cusplets; anteroposteriors of Strasburg (1963); no serrations; premedial show moderate gradient monogrnathic hetero- edge of crown in anteroposteriors convex, post- donty, with teeth becoming smaller, more lateral edge deeply notched forming a low post- oblique-cusped, and lower-crowned towards ends of dental band lateral blade on crown foot; all teeth with a ; posteriormost teeth with strong strong basal ledge and groove, transverse ridges primary cusps; ontogenic heterodonty not known on crown foot; roots low, deep, with transverse at present; gj'nandric heterodonty indicated only by slightly more erect cusp tips on anteroposteriors of adult males. Trunk not markedly compressed, less than twice as high as wide, subtriangular in cross section; a low interdorsal ridge present; lateral dermal keels and precaudal pits absent from caudal peduncle. Dermal denticles of trunk below first dorsal longer than wide, crown with a high, narrow ridge extending to tip of posteriorly directed cusp; a pair of lateral ridges weakly developed or absent, lateral cusps weak or absent. Pectoral fins larger than first dorsal fin in area, their anterior margins about 11,4 times as long as combined base and inner margin lengths; distal tip of adpressed pectoral about over its Figure 3.—lago omanensis. A. Typical teeth: upper, free rear tip when pectoral inner margin is held buccal surface labial surface. B. C. Cross ; lower, Eye. parallel to body axis; origin of pectoral below section of trunk vertebra; thoroughly calcified areas or slightly in advance of fourth gill opening; shown in black. D. Valvular intestine, one side cut away. skeleton less than Drawing by L. J. V. Compagno. pectoral projecting halfway into fin, its longest distal radials about equal groove on attachment surface but transverse in length to corresponding proximal ones; distal notch weak; teeth not noticeably protruding radials with truncate tips and parallel edges. when mouth is closed. Pelvic anterior margins less than half length Dignathic heterodonty very weak, with upper of pectoral anterior margins; pelvic bases equi- anteroposteriors having slightly higher crowns distant between first and second dorsal bases. than lower ones; disjunct monognathic heter- Claspers with pseudoperae, pseudosiphons, odonty indicated by differentiation of medials cover rhipidia, true rhipidia, and exorhipidia in one row on in upper jaw and about 3 lower; (Figures 5B and 5C) ; siphon sacs large, extend- medials smaller, with erect primary cusps, large ing anteriorly to level of pectoral free rear tips premedial and postlateral blades, and no cusi^Iets; (Figure 5A); margins of clasper cartilage larger anteroposteriors are sharji-edged, com- rolled, with margins overlapping to form a tube; pressed, bladelike cutting teeth witli an oblique clasper hooks absent.

618 COMPAGNO and SPRINGER: NEW GENL'S OF CARCHARHINID SHARKS

Origin of first dorsal fin far forward, varying Vertebrae moderately numerous, 129 to 147 in position from above fourth gill opening to in total count {N = 16). Monospondylous pre- slightly before pectoral axilla; midpoint of first caudal (MP) centra 24.5 to 27.6 ^r of total count; dorsal base much closer to pectoral axilla than diplospondylous precaudal (DP) centra 33.6 to to pelvic origins; free rear tip of first dorsal 36.1; and diplospondylous caudal (DC) centra anterior to pelvic fin origins. 37.2 to 40.1 (N =8). A ratios 120 to 162, B

Second dorsal nearly as large as first, its height ratios 102 to 137 (N = 11 ) . DP and DC centra about 70 '"r of first dorsal height; its posterior more numerous than MP centra and nearly equal margin strongly concave. to each other, DP MP ratio 1.22 to 1.46 and Anal smaller than second dorsal, slightly more DC/MP ratio 1.38 to 1.63 (/V = 8). Transition than half its height, its base about % of second between MP and DP centra easily delimited on dorsal base length; its posterior margin nearly radiographs, over pelvic region. Posteriormost straight or shallowly concave; its origin poster- MP centra not greatly hypertrophied. DP cen- to of ior to second dorsal origin by about i/-) \A tra of relatively uniform length throughout, not second dorsal base length; posterior ends of sec- forming a stutter zone of alternating long and ond dorsal and anal bases opposite. short centra. Caudal without projecting ventral lobe-tip in Vertebral calcification pattern a modified ver- adults, preventral margin slightly more than I/3 sion of White's (1937) "Maltese cross" pattern, of dorsal margin length; subterminal margin without diagonal calcified lamellae; notochordal cau- canal long, over half length of terminal margin ; unusually large (Figure 3C); wedgelike dal dorsal margin length about i/o of total intermedialia strongly developed. length; terminal sector of caudal about 1/3 of Supraorbital crest of cranium strongly devel- dorsal margin length; vertebral axis of caudal oped and entire. only slightly raised above body axis. Intestinal valve of spiral type, with about five turns. lago is apparently livebearing (see section in

Reproduction below) , but whether or not a yolk- sac placenta is formed cannot be determined from available specimens.

lago omanensis (NORMAN, 1939)

Eugaleus omanensis Norman, 1939, p. 11, Fig. 3 (type-locality. Gulf of Oman); Compagno,

1970 (generic systematics) .

Galeorhinus omanensis Misra, 1949, p. 21 (in

list of Indian elasmobranchs, name only) ; Fowl- er, 1956, p. 17 (description, after Norman);

1967, p. 363 (in list of fishes of the world, name only).

Figure 5.—lago omanensis. A. Ventral aspect of trunk of mature male to show size and position of clasper MATERIAL siphons. B. Dorsal surface of left clasper. C. Partially left connection expanded tip of clasper. AP, apopyle ; C, between rhipidion and cover rhipidion; CR, cover rhipi- Seven males, 224 to 365 mm; nine females, dion; EG, epirhipidial groove; ER, exorhipidion; HP, 358 to 582 mm (Table 1); holotype, British hypopyle; P-2, pelvic fin; ESA, pseudoperal aperture; Museum (Natural History) Reg. No. 1939.5.24.9, ESP, pseudopera; PSP, pseudosiphon pouch; R, rhipi- a 280-mm female from Gulf of Oman. dion; S, siphon sac; SG, subrhipidial groove. Speci-

619 FISHERY BULLETIN': VOL. 69, NO. 3

Table 1.—Oceanographic data for lago omanensis from Final Cruise Report, Anton Bruun Cruise 4B, Woods Hole Oceanographic Institution (1965).

Lenglh

specimen COMPAGNO and SPRINGER; NEW GENUS OF CARCHARHINID SHARKS

Table 2.—Proportional measurements of lago omanensis expressed as percentages of total lengths; measurement method follows Bigelow and Schroeder (1948). FISHERY BULLETIN: VOL. 69, NO. 3

Pelvic fins somewhat larger than anal but smaller than second dorsal in area; pelvics in some males relatively smaller than those of females; pelvics triangular, with anterior margins slightly convex to nearly straight, apexes broadly rounded to subangular, posterior margins nearly straight, free rear tips acute (slightly attenuate in inner some specimens) , margins straight; pelvic anterior margins 2.6 to 2.8, posterior margins 1.7 to 1.9, and inner margins 1.4 to 1.6 in comparable margins of pectorals. Claspers and associated secondary sexual structures of males generally similar in basic plan to those described for Galeorhimis galeus (as "Galeiis mdgar-is") by Leigh-Sharpe (1921), but differing in several details; claspers long, more slender and more angular distally than those of Galeorhmus with bluntly pointed, flat- Figure 6.— omanensis. Dermal denticles from side lago of males tened tips (Figure 5A) ; claspers adult of trunk below first dorsal fin, 582-mm female, scanning well free rear of electron microscope photomicrograph, scale line at lower extending beyond tips pelvics; left 100 roofed over and closed its equals ^. clasper groove by overlapping sides from apopyle to hypopyle; small pseudosiphon present mediodorsally, its (less than 0.1 mm long) present on anterior part pouch extending anteriorly on clasper. Unlike of palate and inner surfaces of branchial arches, Galeorhimis, the pseudosiphon aperture is much also irregularly and rather sparsely scattered less prominent and is located relatively farther on tongue. from the clasper tip. Cover rhipidion very large Pectoral fins with their in as broad, subangular, (scarcely developed Galeorhinus) , formed anterior margins convex, apexes rounded, post- a rounded flap completely covering rhipidion; erior margins slightly convex, free rear tips rhipidion evenly rounded (wedge-shaped in rounded, and inner margins convex, relatively Galeorhinus); pseudojjera present, dorsolateral short, their anterior margins about an eye di- and opposite to the rhipidion edge (as in Galer- shorter than distance from snout is ameter tips hinus) ; unlike Galeorhinus, the pseudopera to first gill opening; pectoral inner margins long, partially covered by another flap, here termed

about 11/2 to 11/;! times pectoral base length; the exorhi])idion, which originates laterad to the

posterior margin about ll/ij to iy-> times in pseudopera and extends posteriorly to cover part anterior margin; free rear tip of pectoral vary- of the rhipidion. Hypopyle opening at level of ing in position from below posterior end of first pseudopera, cover rhipidion, and anterior third dorsal base to last third of first dorsal base. of rhipidion. Pectoral fin skeleton, as studied on radio- Clasper skeleton studied from radiographs of graphs, somewhat similar to that of Galeorhiniis; six males. Terminology is modified from Junger- propterygium with 1 radial, mesopterygium with son (1899) and White (1936, 1937). One basal 3 or 4, segmented metapterygial axis with 10 to cartilage connecting clasper cartilage to pelvic 12; metapterygial axis elongate, much larger basipterygium; a small beta cartilage present than anterior basals, with a distal set of seg- at the junction of basal cartilage and clasper ments; radials mostly divided into three seg- cartilage; details of terminal cartilages not ments (proximal, intermediate, and distal), clear, but at least two terminals, a dorsal and intermediates shorter than jiroximals or distals, a ventral, are in'esent; clasijer cartilages heavily which are equal in length. calcified in adult males.

622 COMPAGNO and SPRINGER: NEW GENUS OF CARCHARHINID SHARKS

First dorsal fin triangular with height much deepwater sharks, a feature possibly correlated less than length from origin to free rear tip; with habitat). origin ill-defined, grading into predorsal ridge; The chondrocranium was dissected out in one anterior margin slightly concave basally but con- specimen but is not described here. It is similar vex towards fin apex, with a 45 degree slope in structure to the crania of Galeorhiniis and relative to body axis; apex acutely rounded, Mustelus described by Gegenbaur (1872) but posterior margin somewhat concave, free rear differs in numerous details from both. tip slender, elongate, acute; base much longer Stomach very large, subdivided into a sack- than fin height, inner margin about 60 to 70% like fundus and a long slender pylorus. The of fin height; end of first dorsal base about fundus extends posteriorly over two-thirds the over adpressed apex of pectoral; pectoral free length of pleuroperitoneal cavity, then reverses direction as rear tip anterior to pelvic origins by a distance the pylorus to continue anteriorly nearly or quite equal to lengths of pelvic bases. nearly to root of liver, where it joins the spiral Second dorsal fin generally similar in shape intestine. The latter is fusiform, with a spiral to first dorsal; its height about half length from valve of about five turns (Figure 3D). The nar- origin to free rear tip; fin base about 1.4 to 1.5 row rectum has a slender rectal gland attached times height; inner margin about 0.5 to 0.7 of distally to the epigonal organ in both sexes. height; origin of second dorsal posterior to mid- Liver only moderately large, with paired lat- point between anal origin and posterior end of eral lobes concealing small medial lobe, posterior lateral pelvic base; free rear tip of second dorsal op- ends of lobes extending only one-half to posite or slightly posterior to that of anal; sec- two-thirds of distance to posterior end of pleuro- ond dorsal over twice area of anal. peritoneal cavity. Spleen elongate, not nodular, Anal fin a low triangle, with height about 0.4 originating dorsally on distal end of fundus and in length, anterior margin broadly convex, apex coursing anteroventrally on pylorus to spiral in- rounded, posterior margin moderately concave, testine, where it extends posteroventrally to be- the first intestinal free rear tip slender and acute, and inner margin low valve. Pancreas elongate, concave; inner margin almost or quite equal in length to height; fin base 1.4 to 1.6 times fin Table 3.—Vertebral numbers in male and female lago height. omanensis. Dorsal of caudal margin nearly straight, pre- Monospondylous ventral margin broadly convex, and junction of preventral and postventral margins rounded; postventi-al margin long, concave anteriorly but nearly straight posteriorly and curving abruptly upward into subterminal notch; subterminal margin nearly straight, terminal margin invar- iably frayed but apparently moderately concave. Vertebral counts given in Table 3. Vertebral calcification pattern was studied from transverse sections and radiographs of centra from below first dorsal fin. Terminology for vertebral parts follows Ridewood (1921). Primary double cone without diagonal calcified lamellae; solid dorsal, lateral, and ventral intermedialia present, separated by uncalcified areas for the basidorsals and basiventrals (Figure at 3C) ; notochordal canal constricted portion of double cone unusually large (as in many other FISHERY BULLETIN: VOL, 69. NO. 3 veloped and functional in all adult females ex- Thus the specimen is, at least functionally, a amined, with small nidamental •glands almost female. Histological examination of the ovaries obsolete on the right side in some specimens; was not made, but gross examination revealed both testes apparently functional, subequally de- one ripe ovary of normal appearance but little veloped in three males examined, with a single development of the other gonad. A similar in- epigonal organ attached to left testes. Semi- stance of the partial development of claspers by lunar valves of conus arteriosus in two rows, a functional female Centrophoriis bisitanicus the anterior one with three valves, the posterior was reported by Cadenat (1960). A more ex- with three much smaller valves located each on treme example, recorded by King (1966), was the posterior base of an anterior valve. of a hermaphroditic Scyliorhinus canicuhis with Color brownish or grayish above and lighter a single immature clasper, a ripe ovotestis (with below, with no conspicuous markings or abrupt ovarian follicles at all stages and seminiferous color changes from dorsal to ventral; expanded tubules with mature sperm), and functional chromatophores in the darkest specimen give a nidamental glands, oviducts, vasa deferentia, and peppered appearance; small areas of darker pig- seminal vesicles (with sperm). King also listed mentation present near tips of both dorsal and another S. caniculus specimen with two imma- caudal fins and in some specimens extending ture claspers, a ripe ovotestis, and oviducts, but along leading edges of fins; lining of buccal no seminal vesicles and vasa deferentia. The cavity and peritoneum whitish. opposite condition was found in a field-dissected specimen of Mustelus higmani by Dr. John

Thompson (Springer and Lowe, 1963) . This in- VARIATION dividual lacked claspers but had a pair of en- larged testes. The variation in morphometries among our 16 It may be significant that in the above cases specimens is substantial, unusually so for a series the size of each shark was within the range of of adult sharks. Most of the difl'erences do not its functional sex at maturity regardless of ex- follow sex, but it is apparent that the abdominal ternal characters belonging to the opposite sex. section is longer in females than in males. Thus The lago and Centrophoriis females with clasp- the distance between pectoral and pelvic bases ers were larger than would be expected for ma- ranges from 13.7 to 16.1% of total length in ture males of the species, but the clasperless seven males but is 16.8 to 20.0% in nine females. male Mustelus was smaller than mature females This is similar to the situation reported for the of its species. Both hermaphroditic Scyliorhinus squaloid Euprotomicrus bispinatus by Hubbs, were the size of adult females of their species Iwai, and Matsubara (1967) and in Carcharhhuis despite the presence of claspers. leucas by Thorson, Watson, and Cowan (1966). Our smallest male, 224 mm long, is immature Large variations in tooth row and vertebral with uncalcified claspers but six others from counts were noted also. Despite the range of 295 to 363 mm are mature. We did not examine variation between individuals and the sexual internally a 358-mm female, the smallest of its dimorphism in our sample, we find nothing to series, but eight others from 395 to 582 mm are indicate that more than one species is repre- mature and have eggs in their oviducts. The sented or that the variation can be attributed eggs are for the most part not large, having to known geographical or environmental influ- yolks not more than 10 mm in diameter, and ences. in our specimens, embryos, when present, are in a very early stage of development. In the REPRODUCTION oviducts each egg is encased in a thin and soft membranous shell which closely adheres to the One 440-mm specimen in our series has par- oviduct lining. The nidamental glands vary in tially developed and uncalcified claspers but has size from scarcely visible enlargements of the eggs with very early embryos in the oviducts. anterior oviduct to about 10 mm in diameter,

624 COMPAGNO and SPRINGER; NEW GENUS OF CARCHARIIINID SHARKS

but all are far smaller than those present in of ijoorly oxygenated water near the bottom oviparous scyliorhinids. The condition of nida- along the coast between the Gulf of Kutch and mental glands and eggshells indicate that lago the Gulf of Oman (See Banse, 1968, for a gen- omanensis is livebearing, with oviductal egg eral account of the hydrography of part of this counts suggesting a litter of 2 to 10 young. The area). Sharks of species commonly held in ma- relatively small size of egg yolks implies that a rine aquaria are thought to require a high dis- maternal source of nourishment is provided the solved oxygen level for survival although studies embryos unless the young are extremely small at to verify this for particular species have not birth. been made. Low oxygen concentration in water at the bot- SIZE tom, 0.22 to 0.77 ml/liter, is associated with five of the six IIOE stations at which lago omanensis lago is one of the smaller carcharhinids. In was taken. It appears that this be the Carcharhinidae, ScoUodon, the Protozygaeyia species may exceptionally tolerant to low even group in Rhidoprionodon, and Mustelus have spe- oxygen levels, at the moderately warm (16.24° to 22.39° C, or cies nearly or quite as small as /. omanensis, about 61.3° to 72.4° F) water it in- though Eridacnis species are even smaller. One apparently habits. In the Red Sea, Marshall and Bourne of the latter, E. radcliffei, is apparently the smal- reported that their unidentified carcharh- lest carcharhinid and one of the smallest sharks, (1964) inoid be omanensis or a close with males mature at 186 mm and females at (which may lago occurred at 216 mm. relative) depths down to 2195 m. As this area and these depths have Size disparity between the sexes is a common may oxygen concentrations lower than 1 ml/liter at the end phenomenon among elasmobranchs, in all known of summer (Richards, 1957), the Marshall and cases with females larger than males. In lago Bourne shark be able to survive this is may oxygen omanensis disparity very marked ; our levels as low as known lago omanensis appar- largest male (365 mm) was only 63% as long ently does in the Arabian Sea. as the corresponding female (582 mm) and Gibbs and Hurwitz the weighed but one-sixth as much. (1967) regarded great- er development of gill lamellae in the stomiatoid FOOD fish, Chauliodus pammelas compared with that in C. sloani as an adaptation to the low oxygen Stomachs of two specimens contained remains habitat of C. pammelas. We looked at struc- of unidentified fish, in one a fish head 32 mm tures having respiratory functions in lago oman- long and in the other a 50-mm section of the ensis but found nothing to suggest such an posterior trunk of a fish estimated to have been adaptation. /. omanensis, however, has no more than 200 mm long. closely allied species as a basis for comparison. DISTRIBUTION

Table 1 shows the distribution of 16 of 17 ACKNOWLEDGMENTS known specimens of lago omanensis, all except the holotype from IIOE Cruise 4B. Only three We thank Dr. N. B. Marshall, British Museum other shark specimens, all Mustelus sp., were (Natural History) for assistance in comparisons collected during Cruise 4B from 81 trawling of the holotype with specimens of the IIOE ser- stations in the northern Arabian Sea. This total ies, Maarten Korringa, Stanford University, for of only 19 shark specimens of two species is much suggesting the generic name, and Mrs. Martha lower than the expected catch for comparable J. Mitchill of Kent Cambridge Scientific Inc., gear in many other areas of continental shelf and Stanford University, for permitting one of and slope. the writers (Compagno) to use a Cambridge A possible explanation for the low incidence of Stereoscan scanning electron microscope in her sharks in the catches lies in frequent presence care.

625 FISHERY BULLETIN: VOL. 69. NO. 3

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