Paraliparis posteroporus, Stein, 2012

Stein, David L., 2012, Snailfishes (Family Liparidae) of the Ross Sea, Antarctica, and Closely Adjacent Waters 3285, Zootaxa 3285, pp. 1-120 : 95-96

Paraliparis posteroporus n. sp.

Figs. 67, 68

Holotype. NMNZ P.043692, male, 240 mm TL, 219 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.043692/1, cleared and stained right pectoral girdle.

Diagnosis. V 69, D 60, A 54, P 20, notch rays long, some rudimentary. Mandibular pores set well back from symphysis and edges of lower jaw, chin pore pair not in a pit, close together, posterior to symphyseal knob of lower jaw. Teeth almost entirely uniserial except near symphysis. Pectoral fin lower lobe much longer than upper lobe. Radials 4, round, R2 and R3 notched opposite to each other, other radials unnotched. Scapular helve absent, coracoid with deep basal notch.

Description. Counts V 69 (13+56), D 60, A 54, C 6?, P 20 (13+3+4), radials 4 (1+1+1+1), pc ≥6, pore formula unknown. Ratios. HL 18.2, HW 13.6, sn 4.2, E 4.0, orbit 5.6, io ~5.3, uj 6.9, go 2.1, bd ~21, preD 29.0, preA 40.7, sna 13.9, aAf 24.6, UPL 12.1, LPL 15.6, pabd 28.3. In % HL: HW 74.9, sn 23.4, E 22.1, orbit 30.9, io <30.6, uj 38.2, go 11.6, bd ~116, preD 159.8, preA 223.9, sna 76.6, aAf 135.2, UPL 66.3, LPL 89.3, pabd 155.5, cp 4.3, pcl 35.9.

Head less than 1/5 SL, low and compressed, dorsal profile rising evenly from snout through flat interorbital region. Snout short, low, bluntly rounded, projecting slightly beyond upper jaw. Anterior ends of suborbital stays projecting as a prominent strong knob on each side, probably more obvious as a result of damaged snout. Nostrils damaged, apparently close to anterior margin of orbit. Mouth horizontal, subterminal; lower jaw slightly included, oral cleft reaching below anterior half of orbit. Teeth simple, sharp, evenly spaced canines, arranged uniserially for most of jaw length. About 30 premaxillary teeth in a single row, gradually smaller anteriorly before some irregularly bi- or tri- serial teeth near symphysis. Symphyseal gaps present in both jaws; in upper jaw, wide, with a clear notch anteriorly; in lower jaw, narrow, with well-developed symphyseal knob. Eye prominent, orbit large, entering dorsal profile of head, slightly less than 1/3 HL. Gill opening above pectoral fin base and possibly extending over one fin ray, slightly longer than 10% HL; opercular flap a weakly developed shallowly curved lobe, supported by dorsally curved opercle, its tip higher than its proximal end and reaching slightly behind dorsalmost end of pectoral base. Pore formula unknown. Remaining pores of mandibular series normal in size but unusual in arrangement. Chin pores paired, their distance apart about 4% HL, located on mandibular undersurface distinctly posterior to symphyseal knob and well behind tip of jaw. Other mandibular pores located distinctly and unusually close to ventral midline. Suprabranchial pore single, well above gill opening.

Pectoral fins damaged, upper lobe reaching behind midpoint of abdominal cavity, about 2/3 of distance to anal fin origin. Uppermost ray even with or higher than mid-orbit. Upper lobe rounded, of 13 rays, reaching to 1/2–2/3 body cavity length. Notch rays three, right pectoral girdle with two rudimentary and one fully developed ray, all relatively long. Lower lobe long, of three or four rays, the dorsal two filamentous for slightly less than half their length, reaching to below tip of upper lobe and possibly farther; insertion of lowest ray below middle of opercle. No obvious gap present between lower pectoral fin lobes. Right pectoral girdle with 4 (1+1+1+1) moderately large, round, closely and evenly spaced radials of similar size; R1, R4 unnotched, but narrow opposed V notches in R2, R3. Scapular helve absent; coracoid helve long, slender; a deep ventral notch present at base of helve.

Body behind head dorso-ventrally flattened, deepest behind head over mid-abdomen. Dorsal fin insertion between vertebrae 7–8, anal fin insertion between vertebrae 13–14. Dorsal and anal fins gradually deeper posteriorly. Anus anterior, about between bases of lowest pectoral fin lobe rays, anterior to gill opening. Peritoneum clearly visible through body wall. Body cavity short, unusually deep, its dorsal outline humped behind pectoral fin base. Hypural complex fused, slit absent. Caudal fin possibly damaged, apparently of six (3/3) rays, auxiliary rays absent. Pyloric caeca about six, stout, thick walled, of different lengths but none exceptionally long. SECM apparently not well developed. Skin thin, easily damaged.

In alcohol, body dark, head blackish, snout and lower jaw black, blackish brown skin thin and translucent, blackish over ventral surface of body cavity (in addition to black peritoneum visible through body wall); in life, probably completely black from anal fin forward. Pectoral fin lower lobe filamentous rays black. Mouth black, branchial cavity dusky, stomach and pyloric caeca pale except for black remnants of possible blood vessels.

Distribution. Known only from the holotype, collected between 1431–1658 m on the northwest edge of Mawson Bank.

Etymology. The name posteroporus from the Latin postero-, rear, and the Greek porus, hole, denoting the unusual posterior position of the chin pore pair well behind the mandibular symphysis.

Comparisons. The new species is most similar to P. stehmanni but is clearly distinct from it. Although the counts and most of the ratios are similar to P. stehmanni , P. posteroporus differs in pectoral structure, color, chin pore characteristics and depth of body cavity. Its pectoral girdle has four radials, but it has no notches between R1 and R2 (vs notches present), other radial notches small and narrow (vs large and broad), notch rays are well developed and relatively long (vs rudimentary and very short), and the number of notch rays is three or four (vs two). Its body color is solid black anteriorly and dark brown on the tail (vs uniform pinkish violet). In P. posteroporus the chin pores are unusually far posterior on the lower jaw (well behind mandibular symphysis vs near the lower lip) and not in a shallow depression (vs shallow depression in small individuals). Finally, the dorsal outline of the body cavity as expressed by the peritoneum, which is visible through the body wall, is strongly curved (“humped”), making the body cavity very deep (vs shallowly curved). Paraliparis diploprora Andriashev 1986 has very prominent protrusions on the snout, but they are soft tubercles not supported by the suborbitals, and in other regards P. diploprora also does not resemble P. posteroporus .