Seleniolycus robertsi, Peter R. Møller & Andrew L. Stewart, 2006

Peter R. Møller & Andrew L. Stewart, 2006, Two new species of eelpouts (Teleostei, Zoarcidae) of the genus Seleniolycus from the Ross Dependency, Antarctica., Zootaxa 1376, pp. 53-67 : 55-58

Seleniolycus robertsi sp. nov.

(Figs.1, 3a, 4)

Materials. Holotype: NMNZ P.37815, 393 mm SL, female, Pacific-Antarctic Ridge, outer Ross Dependency, north of Balleny and Scott Islands (63°02.0'S, 172°04.0'E), depth 2290 m, longline, FV San Aotea II, Simon Beatson, stn. OBS 1430/242R, 13 May 2001.

Paratypes: (n = 6): BMNH 2006.6.21.1, 348 mm SL, female, Pacific-Antarctic Ridge (65°31.0' to 65°27.0'S, 178°03.0' to 177°57.8'W), depth 1813 m, longline, FV Avro Chieftain, Sydney Thickpenny, stn. OBS 1841/005, 5 December 2003 ; NMNZ P.37819, 357 mm SL, female and ZMUC P766465, 334 mm SL, male, same data as for NMNZ P.37819, Pacific-Antarctic Ridge, north of Balleny and Scott Islands (63°39.0'S, 173°04.0'E), depth 2267 m, longline, FV San Aotea II, Simon Beatson, stn. OBS 1430/ 231R, 9 May 2001 ; NMNZ P.38574, 316 mm SL, male, Pacific-Antarctic Ridge (65°25.5'S, 178°19.5'E), depth 1455-1555 m, longline, FV Janas, Grant Johnson, stn. OBS 1593B/197, 3 May 2002 ; NMNZ P.38804, 354 mm SL, female, Pacific-Antarctic Ridge (65°35.01'S, 177°44'W), depth 1594-1640 m, longline, FV Janas, Stephen Smith, stn. OBS 1728/080, 17 February 2003 ; NMNZ P.39917, 380 mm SL, female, Pacific-Antarctic Ridge (65°27.3'S, 177°57.8'W), depth 1813-1828 m, longline, FV Avro Chieftain, Sydney Thickpenny, stn. OBS 1841/005, 5 December 2003 .

Diagnosis. Differs from congeners by the presence of scales on posterior half of body, a short pectoral fin 7.9-9.4% SL, dorsal fin rays 84-89, and anal fin rays 69-73. It is further diagnosed by the following combination of characters: suborbital head pores 6, preoperculomandibular pores 8; predorsal length 27.1-36.4% SL; snout length 29.8-51.6% HL, eye diameter 11.0-13.0% HL; pectoral fin rounded, 15-16 rays, none exserted; anterior dorsal fin pterygiophore associated with vertebra 6-8; vertebrae 24-26 + 63-71 = 88-97.

Description. Principal counts and measurements are presented in Table 1. Vertebral centra symmetrical, with prezygapophyses and postzygapophyses of equal horizontal length. Anal fin pterygiophores 2 (1-2) inserted anterior to haemal spine of first caudal vertebra. Caudal fin with 1 (1-2) epurals, 4 upper and 4 (4-5) lower hypural rays. Epipleural ribs on 4 (3-4) to penultimate precaudal vertebra. Gill rakers on outer surface of first gill arch simple (not furcate) and with spinules. Branchiostegal rays 6. Pectoral fin relatively short; its origin below body midline; lower rays not thickened. Pelvic fin absent.

Body elongate; trunk relatively slender, tail laterally compressed. Head ovoid, robust; snout broadly rounded. Eyes small, slightly ellipsoid, not reaching dorsal profile of head. Mouth terminal; lower lips without lateral lobe; upper lip continuous across snout. Snout blunt, upper jaw not protruding, reaching posteriorly to about mid-eye or before. Nasal tube well developed, but not reaching upper lip. Gill slit moderate, extending ventrally to base (or just below base) of pectoral fin. Opercular lobe at dorsal margin of gill slit, short, rounded.

Jaw, vomer, and palatine teeth small, conical. Premaxilla with 2 rows. Dentary with 4 (3-4) rows of teeth anteriorly, blending into two rows posteriorly. Vomerine teeth in 2 (2-4) rows. Palatine teeth in 3 (2-4) rows.

Head pores moderate in size; no variation in numbers observed. Postorbital pores 2, located at positions 1 and 4 (sensu Gosztonyi, 1977); nasal pores 2, one set anteromesial to nasal tube, the other posteromesially; suborbital pores 6; preoperculomandibular pores 8, 4 arising from dentary, 1 from anguloarticular and 3 from preopercle; occipital and interorbital pores absent.

Main body lateral line mediolateral, complete to tail tip. Short dorsolateral branch extending from above opercular lobe to near origin of dorsal fin; predorsal branch with widely separated neuromasts extending from above opercular lobe to near caudal fin.

Head and anterior body naked; posterior half covered with up to 40 horizontal rows of small (diameter ca. 0.5 mm), non-overlapping cycloid scales. Dorsal and anal fins naked anteriorly, posterior 1/4 scaled, caudal fin naked. One specimen (BMNH 2006.6.21.1) has a small patch of 33 scales on the otherwise naked abdomen.

Colour. Freshly thawed specimen (Fig. 1a) medium brown, with darker pectoral fin margins. Colour in preserved specimens very similar; peritoneum dark brown, orobranchial chamber and gill rakers pale.

Sexual dimorphism. Measurements of males> females are seen in two males (316-334 mm SL) and five females (348-393 mm SL), with head lengths (18.1-18.8 vs. 16.1-17.6% SL), length of lower jaw (7.1-7.7 vs. 5.4-6.8% SL) and predorsal length (33.5-36.4 vs. 27.1-32.5% SL). Sexual dimorphism in dentition and upper jaw lengths not observed.

Reproduction. The ovary of the only ripening female (BMNH 2006.6.21.1, 348 mm SL) measures 52.3 mm in length. Light orange eggs up to 5.9 mm in diameter.

Etymology. Named in honour of Dr. Clive Roberts, Curator of Fishes, Museum of New Zealand Te Papa Tongarewa, Wellington, in recognition of his valuable contribution to the Biosystematics of Ross Sea fishes project at Te Papa.

Distribution and habitat. Currently known from only seven specimens, all caught on weighted bottom longlines at depths of 1455-2290 m on the southernmost section of Pacific-Antarctic Ridge, north of the Ross Sea, but south of the Antarctic Convergence (63°02' to 65°35'S, 172°04'E to 177°44'W) (Fig. 4).

Comparison with congeners. Seleniolychys robertsi resembles S. laevifasciatus in having a rounded pectoral fin without ventrally exserted rays, and in most morphometric characters (Table 1). It differs, however, by the longer predorsal distance (27.1-36.4 vs. 20.0-23.8% SL), a scaled posterior part of the body (vs. naked), and by having more suborbital head pores (6 vs. 5). It resembles S. pectoralis sp. nov. (see below) in having a scaled posterior body, (although the distance from the snout to the anterior scales is shorter (48.9-55.4 vs. 58.7-61.8% SL)) and in the number of head pores and most other characters (Table 1). But S. robertsi is more slender, has a shorter head (16.1-18.8 vs. 19.8-24.6% SL) and a different pectoral fin shape from S. pectoralis (Fig. 3).