Hymenocephalus nesaeae Merrett & Iwamoto, 2000

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 : 36-37

Hymenocephalus nesaeae Merrett & Iwamoto, 2000

Figs. 14C–E , 16

Hymenocephalus nesaeae Merrett & Iwamoto, 2000: 759 (type locality: 18°53’S, 169°52’E). Material examined. 2 specimens; 1 specimens MNHN 1995-0869 (holotype), 143+ mm TL, 18°53’S, 169°52’E, 919–1000 m; 1 specimen MNHN 1995-0999 (paratype), 130 mm TL, 18°51’S, 168°50’E, 980–990 m.

Diagnosis. Pelvic fin rays 13–14; pectoral fin rays 13–15; snout projecting, 25–30% HL; barbel absent; orbit diameter small, 25% HL; interorbital width 55% HW; infraorbital width 16–17% HL; preopercular supporter moderately long, straight, 6% HL; gill rakers 25–26; ventral striae reaching to about ⅓ from pelvic fin bases to periproct; otolith small with rounded outline, no predorsal lobe developed, colliculi separated, reaching close to anterior and posterior rims of otolith; OL:OH = 1.05; TCL:PCL = 2.8.

Comparison. Hymenocephalus nesaeae resembles H. aterrimus in the large head, the small eyes and the pelvic and pectoral fin ray counts, but differs in the narrower sensory canal systems on the head: infraorbital width 16–17% HL (vs 20–25% HL), supraorbital canal width 10% HL (vs 13–17% HL), preopercular canal width 12% HL (vs 19–23% HL). The preopercular supporter is larger and not forked as in H. aterrimus (infraorbital supporter length 6% HL vs 3–4% HL). The relatively small otolith is characteristic with its rounded outline and the colliculi reaching close to the anterior and posterior rims of the otolith, which resemble otoliths of the genus Coryphaenoides more than they do those of Hymenocephalus . Another similar species is H. papyraceus , from which H. nesaeae differs in pelvic and pectoral fin rays counts (13–14 vs 10–11 and 13–15 vs16–18 respectively), number of gill rakers (24–26 vs 18–22), narrower supraorbital and preopercular canal widths (10% vs 17–20% HL and 12% vs 14–17% HL respectively), longer preopercular supporter (11 vs 6% HL), and the different otolith shape. Hymenocephalus nesaeae represents the most plesiomorphic morphology in the aterrimus group.

Description. Head morphology (n = 1) ( Fig. 14C–D ): Head large, snout projecting, long, (snout length 26% HL), orbit diameter 25% HL, interorbital width 55% HW. Barbel absent. Head canals well developed, large, infraorbital width 16% HL, supraorbital canal with 5 segments, width 10% HL, supratemporal canal narrow, above segments 3 to 4 of supraorbital canal, preopercular canal width 12% HL, postorbital-preopercular interspace 6% HL. Infranasal supporter small; infraorbital supporter short, expanding only beyond rear part of orbit, 60% OD; preopercular supporter moderately long, straight (6% HL).

Otolith morphology (n = 1) ( Fig. 14E ): Otolith smaller than usual for the genus, with round outline and without distinct predorsal lobe; OL:OH = 1.05. All rims smooth and rather regularly curved. Inner face almost flat, with median sulcus. Ostial and caudal colliculi small, terminating very close to anterior and posterior tips of otolith; pseudocolliculum short. CCL:OCL = 0.95; TCL:PCL = 2.8. Dorsal depression indistinct; ventral furrow distinct, moderately close to ventral rim.

Distribution ( Fig. 16 ). So far only known from off Vanuatu.

Figures

FIGURE 14. A–B: Hymenocephalus barbatulus: A—Figure from Gilbert & Hubbs (1920). B—Figure from Cohen et al. (1990). C–E: Hymenocephalus nesaeae: Holotype, MNHN 1995-0869, C—Lateral view of head, D—Dorsal view of head, E—inner face of otolith. F–J: Hymenocephalus papyraceus: F—BSKU 099483, lateral view of head, G—Holotype, USNM 50935, lateral view of head, H—BSKU 099483, dorsal view of head, I—BSKU 44761, inner face of otolith, J—BSKU 44761, ventral view of otolith.

FIGURE 16. Geographical distribution of Hymenocephalus aterrimus, H. barbatulus, H. nesaeae, H. papyraceus and H. sazonovi.