Hymenocephalus megalops Iwamoto & Merrett, 1997

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 : 59-60

Hymenocephalus megalops Iwamoto & Merrett, 1997

Figs. 31A–H , 37

Hymenocephalus megalops Iwamoto & Merrett, 1997: 521 (type locality: 19°36’S, 158°49’E).

Hymenocephalus megalops: Merrett & Iwamoto, 2000: 758 .

Material examined. 35 specimens; 24 specimens AMS I.32433-002, 64–132 mm TL, 10°29’S, 144°01’E, 596–603 m; 1 specimen MNHN 1995-0974 , 184 mm TL, 17°45’S, 168°42’E, 690–750 m ; 5 specimens MNHN 1995-0989 , 91 + – 135 mm TL, 16°33’S, 167°55’E, 602–620 m ; 3 specimens MNHN 1997-0672 , 75 + – 152 mm TL, 14°52’S, 167°03’E ; 2 specimens MNHN 2008-2489 , 91– 124 mm TL, 16°35’S, 167°41’E, 582– 614 m .

Diagnosis. Pelvic fin rays 8; pectoral fin rays 14–16; gill rakers 20–23. Barbel short, 10–15% HL. Orbit large, 41–45% HL. Snout obtuse, slightly protruding, 14–18% HL. Ventral striae extending to about ⅔ to almost the entire distance from pelvic fin bases to periproct. Infraorbital supporter long, 70–90% OD. Otolith very compressed with massive predorsal lobe, OL:OH = 0.75–0.8; colliculi fused; pseudocolliculum long, TCL:PCL = 1.25–1.45.

Comparison. Hymenocephalus megalops differs from other members of the striatissimus Group primarily through the very large orbit (41–45% HL vs 35–40% HL). The otolith is one of the most high-bodied found in the genus with a very massive and intensely ornamented predorsal lobe, which represents a further character useful for the recognition of the species.

Description. Head morphology (n = 3) ( Fig. 31A–C ): snout short, blunt, only slightly projecting, 14–18% HL, orbit diameter very large, 41–45% HL (up to 48% according to Iwamoto & Merrett, 1997), interorbital width 45–60% HW. Barbel short, 10–15% HL, reaching to vertical through anterior rim of orbit. Head canals well developed, infraorbital width 10–12% HL, supraorbital canal width 10–16% HL, preopercular canal with mostly 4, rarely 5 segments, width 12–16% HL, supratemporal canal rarely identifiable, above segment 3 of supraorbital canal, postorbital-preopercular interspace 4–7% HL. Infranasal supporter large; infraorbital supporter long, extended below almost entire length of orbit, 70–90% OD; preopercular supporter moderately long, 5–8% HL, with straight rear margin.

Otolith morphology (n = 6) ( Fig. 31D–H ): Otolith large; OL:OH = 0.75–0.8; OH:OT = 3.0. Dorsal rim with very large and broad, crenulated predorsal lobe, distally marked by vertical incision; posterior tip broadly rounded, positioned at about level of sulcus termination; ventral rim very deep, regularly curved, smooth, deepest anterior of the middle; anterior rim high, nearly vertical. Inner face slightly convex, with median sulcus. Colliculi completely fused, terminating far from anterior and posterior tips of otolith; pseudocolliculum very long. TCL:PCL = 1.25–1.45. Dorsal depression moderately large, moderately indistinct; ventral furrow distinct, close to ventral rim.

Distribution. ( Fig. 37 ) Hymenocephalus megalops is a common species at locations in the Coral Sea off NE- Australia and south of Papua Niugini, Chesterfield Plateau, New Caledonia, Vanuatu to Wallis and Futuna Islands.

Figures

FIGURE 31. Hymenocephalus megalops: A–B—MNHN 1995-0989, A—Lateral view of head, B—Dorsal view of head. C—AMS I.32433-002, lateral view of head. D–H—Otoliths, D—Anterior view, E, G, H—Inner faces, F—Ventral view, D–F—MNHN 1997-0672, G–H—AMS I.32433-002.

FIGURE 37. Geographical distribution of Hymenocephalus aeger, H. megalops, H. striatissimus, H. torvus, H. grimaldii, H. neglectissimus, H. semipellucidus, H. sp. 1 and H.