Hymenocephalus hachijoensis Okamura, 1970

Schwarzhans, Werner, 2014, Head and otolith morphology of the genera Hymenocephalus, Hymenogadus and Spicomacrurus (Macrouridae), with the description of three new species, Zootaxa 3888 (1), pp. 1-73 : 49-50

Hymenocephalus hachijoensis Okamura, 1970

Figs. 23A–D , 27

Hymenocephalus striatissimus hachijoensis Okamura, 1970: 50 (type locality: 33°16’N, 140°03’E).

Hymenocephalus hachijoensis: Okamura, 1984: 93 ; Sazonov & Iwamoto, 1992: 62.

Material examined. 2 specimens BSKU 14171 (holotype), 195 mm TL, and BSKU 14172 (paratype), 130 mm TL, 33°16’N, 140°03’E, 570 m .

Diagnosis. Pelvic fin rays 7–8; pectoral fin rays 14–15; snout barely projecting, short, 15–17% HL; barbel long, 30–35% HL, reaching vertical through center of orbit; orbit diameter large, 35–38% HL; infraorbital width 10–12% HL; preopercular supporter moderately long, with straight rear margin, 6–7% HL; gill rakers 18–20; ventral striae reaching to ½ distance from pelvic fin bases to periproct; otolith with high predorsal lobe, colliculi separated, narrowly placed across collum; OL:OH = 1.05; TCL:PCL = 1.6.

Comparison. Hymenocephalus hachijoensis is readily recognized by the long barbel, which is shorter than in H. longibarbis and H. iwamotoi , of about the same length as in Hymenogadus gracilis , and longer than in any other species of the genus Hymenocephalus , with those of H. aeger coming closest at 20–25% HL. The short, rounded snout resembles species in the striatissimus Group, like the low number of pelvic fin rays (7–8 vs 10–12 in other members of the antraeus Group) and the long infraorbital supporter. The separated colliculi and only moderately enlarged pseudocolliculum easily distinguish H. hachijoensis from species of the H. striatissimus Group. These observations support the concept first expressed by Okamura (1984) to elevate H. hachijoensis to species level.

Description. Head morphology (n = 2) ( Fig. 23A–B ): Snout short, rounded, barely projecting, 15–17% HL, orbit diameter large, 35–38% HL, interorbital width 50–60% HW. Barbel long, 30–35% HL, reaching vertical through center of orbit. Head canals well developed, infraorbital width 10–12% HL, supraorbital canal with 5 segments, width 9–10% HL, supratemporal canal not identified, preopercular canal width 9–10% HL, postorbitalpreopercular interspace 8–10% HL. Infranasal supporter very large, touching upper lip; infraorbital supporter long, expanded beyond entire orbit, 90–100% OD; preopercular supporter moderately long, 6–7% HL, rear margin straight.

Otolith morphology (n = 1) ( Fig. 23C–D ): Otolith large; OL:OH = 1.05; OH:OT = 3.2. Dorsal rim with a distinct, moderately broad predorsal lobe with rounded tip, distally marked by small incision; posterior tip at about level of sulcus termination; ventral rim deep, regularly curved, smooth, deepest anterior of the middle; anterior rim high, nearly vertical. Inner face slightly convex, with slightly supramedian sulcus. Ostial and caudal colliculi moderately small, narrowly placed across collum, terminating moderately close to anterior rim and at some distance from posterior tip of otolith; pseudocolliculum long. CCL:OCL = 0.75; TCL:PCL = 1.6. Dorsal depression small; ventral furrow distinct, moderately close to ventral rim.

Distribution ( Fig. 27 ). Hymenocephalus hachijoensis was originally described only from the type locality off the small Hachijo Island on the Iwo Jima Ridge off southern central Japan. Sazonov & Iwamoto (1992:63) also recorded specimens caught over seamounts of the Emperor Ridge (32°N, 173°E and 41° 04°N, 170°32’E) and on the Kyushu-Palau Ridge (no geographic details recorded).

Figures

FIGURE 23. Hymenocephalus hachijoensis, Holotype, BSKU 14171: A—Lateral view of head, B—Dorsal view of head, C—Inner face of otolith, D—Ventral view of otolith.

FIGURE 27. Geographical distribution of Hymenocephalus antraeus, H. hachijoensis, H. heterolepis and H. punt.