Paraliparis epacrognathus, Stein, 2012

Stein, David L., 2012, Snailfishes (Family Liparidae) of the Ross Sea, Antarctica, and Closely Adjacent Waters 3285, Zootaxa 3285, pp. 1-120 : 52-54

Paraliparis epacrognathus n. sp.

Figs. 35, 36

Holotype. NMNZ P.043690, male, 281 mm TL, 257 mm SL, 71°55.80' S, 173°18.08' E, NW edge of Mawson Bank, R / V Tangaroa, Stn. IPY / CAML TAN 0802 /144, 23 February 2008, 1431– 1658 m. NMNZ P.043690/1, cleared and stained right pectoral girdle.

Diagnosis. V 67, D 60, A 51, C 7, P 21. Lower jaw forming a sharp angle at symphysis; chin pores at symphyseal knob. Teeth primarily uniserial, irregularly biserial near symphysis. Upper and lower jaws long, 53% HL. Pectoral fin notch rays present as rudiments reduced to bases only. Radials 4 (3+1), R1 and R3 smaller than R2 and R4. Coracoid notch absent.

Description. Counts. V 67 (13+54), D 60, A 51, C 7, P 21, pc 5, pore formula unknown. Ratios. HL 17.2, HW 12.3, HD 15.8, sn 5.1, E 3.6, uj 9.2, go 1.9, preD 26.2, preA 41.9, ma 11.9, aAf 27.7, UPL 14.4, LPL 14.2% SL. In % HL, HW 71.7, HD 91.6, sn 29.4, E 21.0, orbit 26.5, uj 53.4, go 11.3, ma 69.2, preD 152.5, preA 243.4, sna 80.3, aAf 161.1, UPL 83.7, LPL 82.8, LLD 11.3, cp 3.8.

Head deep and compressed, dorsal profile flat, rising steeply from rounded snout to above preopercle; snout low, rounded, projecting a short distance anterior to upper jaw. Nostrils pore-like with thickened rim, opening a short distance anterior to orbit, slightly below horizontal through center of pupil. Mouth subterminal, horizontal, oral cleft reaching to below front of pupil; teeth in both jaws sharp canines. Premaxillary teeth in uniserial row of about 34 except irregularly biserial near symphysis; teeth smaller anteriorly. Mandibular teeth similar but with fewer irregular additional teeth near symphysis. Clear symphyseal gaps in both jaws. Lower jaw triangular, symphysis an acute angle defined by a deep joint. Eye and orbit moderately large, prominent in head; upper edge of orbit defined by interorbital profile but not entering it. Gill opening completely above pectoral fin; opercular flap small, rounded, supported by horizontal crescent-shaped opercle, its tip pointing dorsally. Mandibular pores pale, rims thickened; symphyseal pore pair close, slightly more than one pore diameter apart, located far anteriorly at ventral end of lower jaw symphysis. More posterior mandibular pores larger and more obvious. Remainder of cephalic pores damaged, pore formula unknown.

Pectoral fin distinctly shorter than head, reaching slightly more than half way to abdomen end, its upper ray above a horizontal through mid-pupil. Upper lobe a little more than 80% head, lower lobe of similar length, notch deep, two rudimentary rays present as bases only. Pectoral ray formula 14+3+4, rays in upper and lower lobes distinctly more closely spaced than rays in notch, which are very widely separated from each other. Lower lobe rays free for about half their length. Distance between lower lobes more than 10% head length. Pectoral radials 4 (3+1), small, rounded, oddly sized, R2 and R3 notched. R1 unusually small, R2 much larger, ventral notch sharp and triangular; R3 smallest with broad shallow dorsal notch; R4 largest, round. Scapula axe-shaped, basal plate broadest. Coracoid helve long and slender, ventral basal notch absent, one fenestra in base.

Body gradually tapering from above middle of pectoral fin. Anus located below posterior part of opercular flap. Abdominal cavity long, deep. Predorsal length more than 1 1/2 head length, first dorsal fin pterygiophore insertion between vertebrae 8–9, anal fin insertion between vertebrae 14–15. First anal fin ray rudimentary. Caudal of seven rays (3/4), auxiliary rays absent. Pyloric caeca digitate, matted and flattened against stomach.

Color of skin in alcohol dusky rose, darker anteriorly and ventrally. Pectoral fin upper lobe black-edged, lower lobe rays mostly black. Oral cavity dusky, tongue somewhat paler; branchial cavity blackish, peritoneum black, stomach and pyloric caeca pale.

Distribution. Known only from the holotype, collected off the northwest edge of Mawson Bank, Ross Sea, at 1431–1658 m.

Etymology. From the Greek epakros, pointed at the end, and gnathos, jaw, to denote the sharply angled lower jaw symphysis.

Comparisons. Because of its primarily uniserial teeth, Paraliparis epacrognathus is most likely to be identified as P. stehmanni , P. copei sensu lato, or P. neelovi . It differs clearly from P. stehmanni in the absence of the large radials with very deep notches and fenestrae, fewer vertebrae (67 vs 69–71), shorter gill opening (11 vs 15– 17% HL), shorter mandible to anus distance (12 vs 13–17% SL) and other characters. Its gill flap (vs none), angular lower jaw symphysis (vs rounded), and anterior chin pore location distinguish it easily from P. copei . In addition to having four rather than three radials it differs from P. neelovi in having seven (vs six) caudal rays and many proportional ratios just outside the ranges of those of the latter. It could also be mistaken for P. longicaecus or P. plicatus (see below).

Comments. The endochondral plate and radials of P. epacrognathus may be unique in the genus ( P. meganchus Andriashev 1982b has small radials, but they are noticeably larger), but they may also be anomalous and restricted to this individual. In particular, the small sizes of R1 and R3, and the shallow dorsal notch in R3, are unlike the usual pattern in liparids, in which the size of the dorsal two or three radials decreases ventrally. In addition, where notches are present in the radials, they are usually either triangular or narrow slits, unlike that of R 3 in this species. However, regardless of whether these particular characters are anomalous, other characters support designation of the species as new: the sharply angled lower jaw, anterior position and arrangement of the chin pores, presence of four radials in a 3+1 pattern, seven caudal fin rays, and the combination of other characters. Even if this specimen had only 3 radials (2+0+1) it would still not match any described species, owing to its seven caudal rays, chin and chin pore arrangement, and other characters.

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