Pachycara brachycephalum

Pachycara brachycephalum (Pappenheim, 1912)

Lycodes brachycephalus Pappenheim, 1912: 179, pl. X, fig. 3 (type locality: Davis Sea).

Austrolycichthys brachycephalus: Regan, 1913: 244, fig. 2; Norman, 1938: 81, 83.

Pachycara brachycephalus: Anderson, 1988: 74, fig. 16.

Pachycara brachycephalum: Anderson, 1990b: 274, fig. 22.

Material examined. Weddell Sea: MNHN 1990-635 (1 specimen; 210 mm SL), 72°55.0'S, 19°49'W, 617 m, POLARSTERN sta. 269, Feb. 1989, W. Arntz. ISH 9/91 (1; 150 mm SL), 72°53.3'S, 19°34.7'W, 481 m, POLARSTERN, ANT V/3, 20 Oct. 1986, W. Ekau. ISH 16/91 (2; 105-251 mm SL), 72°51.4'S, 19°41.4'W, 460 m, POLARSTERN, ANT V/3, 8 Nov. 1986, W. Ekau. South Orkney Islands: USNM 356658 (3 specimens; 230-311 mm SL), 60°45.5'S, 48°13.5'W, 2511-2542 m, ISLAS ORCADAS coll. UMO 116, 18 Feb. 1976, H. H. DeWitt. South Shetland Islands: SAM 34531 (5; 250-354 mm SL), 61°42.0'S, 55°05.9'W, 2227-2234 m, POLARSTERN sta. AGT 111, 14 Dec. 1996, K.-H. Kock Ross Sea: RUSI 54819 (3; 210-240 mm SL), 72°59.8'S, 175°08.6'E, 360 m, N.B. PALMER 96-6, 18 Dec. 1996, J. T. Eastman. RUSI 54821 (3; 205-217 mm SL), 75°30.1'S, 174°56.8'E, 300 m, N. B. PALMER 96-6, 3 Jan. 1997, J. T. Eastman. RUSI 54825 (32; 184-253 mm SL), 77°59.0'S, 177°58.9'E, N. B. PALMER 96-6, 24 Dec. 1996, J. T. Eastman.

Diagnosis. Pachycara brachycephalum is distinguished from its congeners by the following combination of characters: pelvic fins present or (rarely) absent; branchiostegal rays 6; no occipital pores; lateral line with ventral and mediolateral branches, ventral originating behind posteriormost postorbital pore, mediolateral originating on vertical through pectoral fin margin or somewhat anterior to margin when fin appressed; gill rakers blunt and triangular except in specimens over about 320 mm SL; vertebrae 20-27 + 71-86 = 92-113.

Remarks. This species was thoroughly redescribed on the basis of 76 specimens, including four syntypes, by Anderson (1988). All of these possessed the typical, rudimentary pelvic fins of most zoarcids. The new Weddell and Ross seas material adds no further data except the following: Pelvic fins are absent in RUSI 54819, MNHN 1990-635, one (105 mm SL) in ISH 16/91, 28 in RUSI 54825 and one (217 mm SL) in RUSI 54821. The other in ISH 16/91, ISH 9/91, MNHN 1990-633, 1990-634, two (205, 214 mm SL) in RUSI 54821 and four (202-228 mm SL) in RUSI 54825 have regressed, nipple-like pelvic fins as described for P. rimae by Anderson (1989). Five zoarcid species are now known in which pelvic fins are present or absent (others are Pachycara mesoporum, P. sulaki, Lycenchelys monstrosa and Crossostomus chilensis (Anderson, 1994: 13).

Pachycara goni from the Weddell Sea was diagnosed in part on its furcate gill rakers, like those of the West African P. crossacanthum (Anderson, 1989, 1991). Three specimens of P. brachycephalum in SAM 34531, 322-356 mm SL, the largest known, had furcate gill rakers as well, thus this state seems to have an ontogenetic component in P. brachycephalum. However, P. goni (single known specimen at 262 mm SL) is distinguised from P. brachycephalum by its higher vertebral and unpaired fin-ray counts (vert. 27 + 98; D 118; A 99), seven suborbital pores and more posterior origin of the mediolateral lateral line. Specimens USNM 356658 of P. brachycephalum had the dorsal-fin origin associated with vertebrae 8-9, extending this character from vertebrae 3-7 (Anderson, 1988) to vertebrae 3-9. These also extend the lower depth range from 1810 m (Anderson, 1988) to 2542 m, overlapping that of the presumed lower-slope Pachycara goni (Anderson, 1991), caught at 2025-2037 m.