Ventichthys biospeedoi, Jørgen G. Nielsen, Peter Rask Møller & Michel Segonzac, 2006

Jørgen G. Nielsen, Peter Rask Møller & Michel Segonzac, 2006, Ventichthys biospeedoi n. gen. et sp. (Teleostei, Ophidiidae) from a hydrothermal vent in the South East Pacific., Zootaxa 1247, pp. 13-24 : 16-23

Ventichthys biospeedoi , new species

(Figs. 1-8)

Ophidiidae: Geistdoerfer 1996, fig. 6.

Materials

Holotype: MNHN 2004-2037, 266 mm SL, male, South East Pacific Rise, hydrothermal vent site Oasis, 17°25.38’S, 113°12.29’W; BIOSPEEDO cruise, submersible Nautile, R/V Atalante, dive PL 1582, baited trap B2, depth 2586 m, 22 April 2004, collected by Michel Segonzac.

Paratype: MNHN 2004-2038, 282 mm SL, sex unknown, same data as for holotype. Prior to the taxonomic examination the paratype had been eviscerated so that only the kidneys remain.

Diagnosis

See generic diagnosis.

Description

The principal meristic and morphometric characters are shown in Table 3. Where there are differences between the holo- and the paratype those of the paratype are given in brackets.

Body short and compressed, snout blunt; small, oval, imbricate scales covering body, head and proximal part of dorsal, caudal, anal and pectoral fins; ca. 250 scales in a line from upper part of gill slit to base of caudal fin; dorsal fin origin above hind margin of pectoral fin, anal fin origin slightly behind midpoint of fish, pectoral fin short and rounded, and longest pelvic fin ray reaching one fourth the distance from its base to anal fin; length of head about twice in preanal length; horizontal diameter of eye 1.5 times in length of snout; anterior nostril placed midway between upper lip and posterior nostril, both nostrils with a low rim; upper jaw ending just behind eye, maxillaries partly sheathed posterodorsally; a strong opercular spine well hidden by skin; anterior gill arch (Fig. 2) with 5(3) knobs on upper branch, one long raker in the angle and lower branch with 10(9) long and 6 knobs; 65 gill filaments, longer than the long gill rakers; length of the 2 pseudobranchial filaments about half eye diameter.

Dentition (Fig. 3). All teeth small and conical; premaxilla with 5 rows anteriorly at symphysis, merging into 3 rows posteriorad; vomer horseshoe-shaped, with 13(25) teeth in 2-3 rows; palatines with 6(5) rows of up to 15(19) teeth; dentary with 4 rows anteriorly at symphysis, merging into 2 rows posteriorad. One median basibranchial tooth patch with rather weak teeth.

Head pores (Fig. 4). Supraorbital pores 1 placed above opercular flap (often termed “first lateral line pore” - see Møller et al., 2004, p. 145); infraorbital pores 5(3 anterior and 2 posterior), the posterior one the largest; mandibular pores 5(2 anterior and 3 posterior), the second anterior pore from both sides with joint opening, the posterior pore large with low rim; preopercular pore 1.

Lateral lines (Fig. 4). Four rows of small, tube-shaped, widely separated neuromasts. A short row in front of the dorsal fin with 12(10) neuromasts, a row below the entire dorsal fin with 45(44) neuromasts, a median row from the vertical through the anal fin origin to the origin of the caudal fin with 15(14) neuromasts, and a ventral row from the vertical through the anal fin origin to origin of the caudal fin with 15(12) neuromasts. The small neuromasts are very difficult to observe having a colour similar to the body.

Sagittal otolith (Fig. 5). Sagitta oval and thick, 1.5 times as long as high and 3 times as long as thick. The large sulcus is undivided and much wider anteriorly than posteriorly. The dorsal rim is flat with a pronounced postdorsal angle.

Axial skeleton (Fig. 6). Tips of neural and haemal spines pointed; first neural spine half the length of second spine; vertebrae 4-9 with somewhat depressed neural spines; bases of vertebrae 5-12 enlarged; parapophyses on posterior 9 precaudal vertebrae; pleural ribs on vertebrae 3-17(3-16); epipleural ribs on vertebrae 5 through 16 (4 through 15).

Internal organs. The 15 mm long and 5 mm broad testes are joined in a spindle-like shape similar to the ovaries in many other ophidiiform species. Histological sections showed, however, typical unripe testicular tissue. The kidneys are unusual by being located posterior to the thick-skinned swimbladder and by forming a large, compact, darkblue body posterior-most in the abdominal cavity (Fig. 7); histological sections of the “body” from the paratype proved to be kidney tissue. The large stomach almost reaches the anal opening and the short intestine forms four coils. One thick pyloric coecum.

Coloration. After one year of preservation the specimens are light brown to whitish with bluish eyes. Photos of Ventichthys biospeedoi specimens taken in situ show a greyish coloration.

Biology

The holotype, a male with spindle-formed, unripe testes, does not contain any identifiable stomach contents. The paratype was eviscerated only leaving the strangely formed kidneys which may be an adaptation to the special conditions near the vents. The capture of the two specimens in a baited trap indicates a necrophagous diet. Fig. 8A shows specimens grazing on the bottom. The poorly developed teeth and the presence of 10-11 long gill rakers on the anterior arch indicate that it preys upon rather small food-items. The thick skin could be an adaptation to endure the high temperatures in the hydrothermal vent area. The same condition is found in another vent-fish, Thermichthys hollisi . The presence of a male without an intromittant organ shows that it is oviparous.

Habitat

The vent site Oasis is composed of active black smokers covered with the tubeworm polychaete Alvinella spp., large patches of mussels, clams and stalked cirripeds. A milky fluid diffuses from crevices and collapsed lava lakes, with clouds of swimming amphipods. The two specimens here studied were collected next to such a hole (Jollivet et al., 2004, fig. 3), surrounded by the mytilid mussel Bathymodiolus thermophilus Kenk & Wilson, 1985 , the clam Calyptogena magnifica Boss & Turner, 1980 , the stalked barnacle Neolepas cf. zevinae Newman, 1979 , actinostolid sea-anemones ( Chondrophellia-like ), the bythograeid crab Bythograea thermydron Williams, 1980 , the galatheid crab Munidopsis sp. and a recently described nematocarcinid shrimp, Nematocarcinus burukowskyi Komai & Segonzac, 2005 . Other fish occur in this environment such as the synaphobranchid Ilyophis saldanhai Karmovskaya & Parin, 1999 , the bythitid Thermichthys hollisi (Cohen et al., 1990) and an unidentified hagfish. Additional V. biospeedoi specimens were observed at other sites (see “Distribution”) visited during the BIOSPEEDO cruise, between 2585 and 2840 m (Jollivet et al., 2004), at places sometimes ten or more individuals swimming in the shimmering vent fluids with temperatures between 2 and 7°C (Fig. 8B).

Distribution

Known only from the South East Pacific Rise, where it was caught on hydrothermal vent site Oasis (17°25.38’S, 113°12.29’W, 2586 m) and observed on three additional sites: Yaquina (7º25’S, 107º48’W, 2750 m) , Hobbs (17º35’S, 113º15’W, 2595 m) and Gromit (21º34’S, 114º18’W, 2840 m) .