^>euo BREVIORA MnaseTLaim of Compsirative Zoology Cambridge, Mass. December 31, 1963 Number 196 A NEW GENUS AND SPECIES OF BATHYPELAGIC OPHIDIOID FISH FROM THE WESTERN NORTH ATLANTIC By Daniel M. Cohen U. S. Fish and Wildlife Service Washington, D. C. Through the kindness of Dr. Richard H. Backus of the Woods Hole Oceanographie Institution and Dr. Giles W. Mead of the Museum of Comparative Zoology I have had the opportunity to study the three fishes reported upon below. Although they were taken off the southern edge of Georges Bank, hardly a zoologically unknown area, they represent the first of their kind ever captured. And, indeed, they are so different from any other known ophidioid that still another name must needs be added to the already lengthy roster of genera in this group. ThaLASSOBATHIA gen. nov. Diagnosis. Chin barbel absent. Vertical fins continuoiLS; ventral fins each with two rays, originating close to the level of the posterior margin of the preopercle and a short distance behind the symphysis of the cleithra ; the ventral fins covered with thick skin, short, extending only to the level of the origin of the pec- toral fin; pectoral fin rounded, without separate elongated rays. Branchiostegal membranes separate ; gill rakers reduced in num- ber and size ; branchiostegal rays seven. Preopercular spine pres- ent beneath skin. Anterior nostril lacking a tube, placed high on snout. Teeth present on premaxillary, vomer, palatine and dentary, lacking on basibranchials. Maxillary not expanded pos- teriorly, not sheathed. Premaxillary not protractile, bound to the snout anteriorly by a broad frenum. Head compressed, its height greater than its width. Eyes well developed. Body compressed, relatively short and stubby. Two lateral lines. 2 BREVIORA No. 196 Peritoneum dark. Swimbladder reduced, its cavity completely occluded ; bladder not bolind to vertebrae. Neural spines on abdominal centra not depressed ; their tips not truncate. Type species. Thalassohatlua pclagica sp. nov. The name Thalassohathia is derived from the Greek GaXaaaa, the sea ; ^aO'jq, deep. The gender is feminine. Relationships. The main problem encountered in establishing this genus has been to determine its relationships rather than to distinguish it from any presently known genera. The curiously reduced ventral fins and the general shape and consistency of the body might suggest relationship with the liparid fishes ; however, there is not the slightest trace of either a suborbital stay or a sucking disc. In addition, the branchiostegal membranes are sep- arate from each other and from the isthmus, and the gill opening extends far up on the side of the body in typical ophidioid fashion. The last character also separates ThalassohafJiia from the Zoarcidae (not including Lycodapus) . The non-protractile premaxillaries and attached broad frenum suggest the condition of the upper jaw found in salariine blennnies ; however, very different dentition, branchiostegal membranes, ventral fins, caudal fin connections and other characters separate Thalassohathia from the Salariinae. In addition, the absence of a one-to-one correspondence between dorsal and anal fin rays and vertebral centra separates Thalassohathia from any of the blennioids. Among the ophidioids the closest known relatives of Thalasso- hathia appear to be the Bythites — Oligopus — Cataetyx group of genera recently discussed by Cohen (in press). Some reasons for deriving Thalassohathia from this group are the similarly compressed and foreshortened body, the typical bythitine denti- tion, and especially the double lateral line system, which greatly resembles that found in some of the species of Oligopus (Cohen, in press). Although at first glance Thalassohatlna does not appear to be a bathypelagic fish, closer examination reveals that many of its characteristics are adaptations to a midwater life. The skeleton is so poorly ossified that X-ray photographs are very indistinct. Scales are completely lacking. The swimbladder is a small, tissue- filled organ similar to those which have been found in many other species of bathypelagic fishes. The above characters and their significance in floating fishes have been treated by Denton and Marshall (1958) and Marshall (1!)()0). Other structures wbich may help to keep Thalassohathia aloft are its subdermal fatty 1963 NEW OPTTIDIOID FISH 3 layer and enlarged liver. Among the most characteristic features of ophidioid fishes are the naked ventral fin rays which probably serve as tactile organs in benthic species (Herald, 1953, and serve as tactile organs in benthic species (Herald, 1953 and Briggs and Caldwell, 1955, have confirmed this for two species of benthic Ophidiidae). These structures would of course be useless in midwater, and Thalassobathia has reduced ventral fin rays which are covered with thick skin. Because of its midwater habitat, Thalassohathia should also be compared with the ophidioid subfamily Aphyoninae (Nybelin, 1957) which comprises a small group of bathypelagic species. Aphyonines are small, pale fishes with thin, scaleless skin, weak musculature, reduced ossification and no swimbladders. Although they are livebearing, they have a copulatory apparatus which is very different from that found in benthic livebearing ophidioids. They also lack well developed eyes and lateralis systems. I believe that neoteny has played an important part in the evolution of the aphyonines. Tlialassuhathia , with its large eyes, well devel- oped lateralis system and bythitiiie dentition, seems, on the other hand, to be one more offshoot of the highly adaptive Bythites group of genera, and although it shares a common environment with the Aphyoninae, the two are not at all closely related. Specimens examined in preparing the foregoing section are listed in Cohen (in press). In addition I have examined the aphyonine material described by Nybelin (1957), specimens of Aphyonus in the Museum of Comparative Zoology and in the British Museum (Natural History), and specimens of Bara- thronus in the U. S. National Museum and the Chicago Natural History Museum. I thank the fish curators in Cambridge, Chi- cago, Goteborg, London and Washington for their kindness. Thalassobathia pelagica sp. nov. Figures 1, 2 Holotype. MCZ 42161, 221 mm standard length, collected by Richard H. Backus on board the "Capt. Bill III," haul RHB 913; October 13, 1962; 39° 26' N., 71° 00' W. to 39° 32' N., 71° 00' W.; depth to gear 390 fms. (approx. 713 m), depth to bottom 1400-1350 fms. (approx. 2561-2469 m) ; time 1020 to 1505 hrs. EDT ; 64 foot open midwater trawl. Paratypes. MCZ 42162 (2) ; data as for the holotype. Description. Body compressed and foreshortened, greatest depth between three and four in total length. Head relatively BREVIORA No. 196 S3 O tB .9 O t-i be a> a S a o o 'Si Si. e e o =0 =0 e e 2 1963 NEW OPIIIDIOID FISH 5 short, between five and six in total lengtli. Snout rounded, nioutli slightly inferior. Interoi-bital area flat or slightly convex. Out- lines of head converging anteriorly when viewed from above. Eye prominent, horizontal diameter of cornea about three and one-half in head. Posterior nostril an elongate slit immediately in front of ventral half of eye, anterior nostril small and round, closer to tip of snout than to orbit. Body quite flexible due to weak ossification, feeling much the same as icosteid fishes. All fins covered M'ith thick skin. The dorsal fin appears to originate a short distance behind the level of the posterior margin of the opercle ; it is preceded by rayless pterygiophores and ptery- giophores bearing very reduced rays. The exact number of these elements is in doubt as their weak ossification makes them difficult to count on an X-ray photograph. Pectoral fins inserted ver- tically, broadly rounded; in the holotype and smallest paratype the pectoral fin extends about two-thirds of the way from its origin to the vent, in the other paratype the pectoral fin extends only about one-half of the pectoral origin to vent distance. The ventral fins much reduced and covered with thick black skin (Fig. 2C), the longer, inner ray extending only slightly beyond the level of the base of the pectoral fin. One pectoral fin was cleared and stained to verify the number of rays. Teeth short, needle-like, extending on the dentary in a single line from the angle of the gape to the symphysis, where a broader patch of teeth is present ; premaxillary teeth arranged similarly to those on the dentary ; vomerine teeth in a roughh- circular patch; palatine teeth in an elongate patch, about three or four times longer than wide. Suprabranchial tooth patches present; however, I have been unable to find any basi-branchial teeth. Tongue massive, lacking teeth and lacking an anterior prow-like extension. The first gill arch with rakers reduced to a few fleshy flaps and protuberances laterally (Fig. 2A), medially (Fig. 2B) with seven or eight small rakers. A prominent pseudobranch located lateral to the upper arm of the first arch. Gill filaments of moderate length, about equal to diameter of lens. Color brown-grey over the body, the grey due mainly to a mucous coat ; the fins and head darker. Prominent pores on the head. The lateral canal w4th a single pore near the upper angle of the opercle ; supraorbital canal with two or three pores, one above the upper nostril, another below and slightly ahead of the upper nostril, a median pore in the interorbital region of the largest paratype ; infraorbital canal BREVIORA No. 196 Fig. 2. Thalassobathia pelagica. A, First gill arch from left side of smallest paratype, lateral view. B, First gill arch from left side of smallest paratype, medial view. C, Ventral fins of largest paratype. Drawn by Mildred H. Carrington. i 1963 NEW OPHIDIOID FISH 7 with nine pores, the anteriormost below the anterior nostril and immediately behind one of the supraorbital pores, six in an irregular row in the loose skin above the upper jaw, and two behind the eye ; preoperculo-mandibular canal with five or six pores located along the ramus of the lower jaw; in the smallest paratype the pair of pores located closest to the midline of the lower jaw have joined to form a single pore. Lateral line with an upper and lower section, the upper line originating above the opercle and arching upward and back to the level of the origin of the dorsal fin, where it extends pos- teriorly about midway between the dorsal profile and the midline ; the dorsal line disappears at about two-thirds of the distance between the posterior margin of the opercle and the base of the tail; the ventral line originates slightly behind the level of the vent and extends posteriorly to the tail in the midline of the body. Each of the two lateral lines along the body is marked by about 30, small, dark, papillae ; similar structures are sparsely dis- tributed over the body and head. Each specimen has a broad, fleshy hood over the genital area. The largest paratype has a pair of large ovaries which contain small eggs at the bases of numerous villi. The smallest paratype contains small paired ovaries with developing eggs. The swimbladder of the smallest paratype is a white, bean- shaped organ about 14 mm long. The lumen appears to be com- pletely occluded by white tissue.^ The liver is prominent in both paratypes, and the thick skin has a subdermal fatty layer. The brain case is cartilaginous. The olfactory nerves extend anteriorly in the orbit and are separated from each other by the cartilaginous interorbital. All three specimens bear numerous round marks left by squid tentacles. The smallest paratype has the top of its head bitten off. LITEEATURE CITED Briggs, John C. and David K. Caldwell 1955. The characteristics and distribution of the spotted cusk eel OtopJiidium omostigmum (Jordan and Gilbert). Quart. Journ. Florida Acad. ScL, 18(4) : 285-291. 1 I am indebted to N. B. Marshall for his kindness in examining the swim- bladder. 8 BREVIORA No. 196 Cohen, Daniel M. (in press). A review of the ophidioid fish genus Oligopus with the descrip- tion of a new species from West Africa. Proc. U. S. Nat. Mus. Denton, E. J. and N. B. Marshall 1958. The buoyancy of bathypelagic fishes without a gas-filled swim- bladder. Journ. Mar. Biol. Assoc. U. K., 37: 7.')3-767. Herald, Earl S. 1953. Spotted cusk-eel, the strange fish that stands on its tail. Cali- fornia Fish and Game, 39(3): 381-384. Marshall, N. B. 1960. Swimbladder structure of deep-sea fishes in relation to their systematics and biology. Discovery Eepts., 31 : 1-122. Nybelin, Orvar 1957. Deep-sea bottom fishes. Eepts. Swedish Deep-Sea Expedition 2, zoology (20) : 250-345, pis. 1-7. Table 1 Counts and measurements in mm of Thalassobathia pelagica Ilolotype Paratypp Parafyiic Dorsal rays Anal rays Pectoral rays Vertebrae'^ Caudal rays Standard length Head length Snout Orbit Interorbital Upper jaw length Preanal Greatest body depth Body depth at vent Pectoral fin length 1 Not including hypural.