Hymenocephalus heterolepis ( Alcock, 1889 )

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 : 50-52

Hymenocephalus heterolepis ( Alcock, 1889)

Figs. 24A–M , 27

Macrurus heterolepis Alcock 1889: 396 (syntypes from: Andaman Sea, off Ross Island, and Bay of Bengal , between North and South Sentinel Islands).

Macrurus (Mystaconurus) heterolepis: Alcock 1891: 122 and 309 (figure).

Macrurus (Mystaconurus) cavernosus: Alcock 1899: 117 (records from Andaman Sea only).

Hymenocephalus heterolepis: Iwamoto in Cohen et al. 1990: 231.

Material examined. 114 specimens; 1 specimen BMNH 1890.7 .31.6 (syntype), about 120 mm TL, Andaman Sea , off Ross Island ; 98 specimens CAS 50132, 83 + – 121 mm TL, 10°39’N, 96°34’E, 367–375 m ; 15 specimens CAS 50124, 91 + –120+ mm TL, 10°39’N, 97°06’E, 293 m .

Diagnosis. Pelvic fin rays 10–11; pectoral 11–13; gill rakers 22–25. Barbel short, 5–10% HL, not reaching vertical through anterior rim of orbit. Orbit 28–32% HL. Snout pointed, protruding, 17.5–20% HL. Ventral striae extending to about ⅔ the distance from pelvic fin bases to periproct ( Fig. 24F ). Otolith compressed, OL:OH = 0.9–0.95; colliculi separated, small, narrowly placed across collum; pseudocolliculum long, TCL:PCL = 1.5–1.7.

Comparison. Hymenocephalus heterolepis resembles H. italicus , with which it commonly has been synonymized (first synonymized with H. cavernosus by Alcock (1899), see below under H. italicus ) and the new species H. punt described in the following. From H. italicus it differs in the smaller orbit (28–33 % HL vs 35–40% HL) and the separated colliculi of the otolith (vs joined). The additional distinguishing character of the otoliths supports the recognition of the species. For distinction from H. punt n.sp. see below.

Description. Head morphology (n = 4) ( Fig. 24A–E ): Snout moderately long, pointed, projecting, 17.5–20% HL, orbit diameter small, 28–32% HL, interorbital width 60–65% HW. Barbel short, 5–10% HL, not reaching vertical through anterior rim of orbit. Head canals well developed, infraorbital width 12–16% HL, supraorbital canal with 5 to 6 segments, width 12–15% HL, supratemporal canal rarely observable, above segment 4 of supraorbital canal, preopercular canal width 13–15% HL, postorbital-preopercular interspace 6–8% HL. Infranasal supporter moderately large; infraorbital supporter short, expanding only beyond rear part of orbit, 35–70% OD; preopercular supporter moderately long, 6–8% HL, with straight rear margin.

Otolith morphology (n = 7) ( Fig. 24H–M ): Otolith large; OL:OH = 0.9–0.95; OH:OT = 3.2–3.5. Dorsal rim with large, very broad, somewhat crenulated predorsal lobe with mostly pointed tip, distally inclining to posterior tip without marked incision; posterior tip at about level of sulcus termination; ventral rim deep, regularly curved, smooth, deepest anterior of the middle; anterior rim high, subvertical to nearly vertical. Inner face slightly convex, with median sulcus. Ostial and caudal colliculi small, narrowly placed across collum, terminating far from anterior and posterior tips of otolith; pseudocolliculum long. CCL:OCL = 0.9–1.3; TCL:PCL = 1.5–1.7. Dorsal depression moderately large, indistinct; ventral furrow distinct, moderately close to ventral rim.

Discussion. Alcock (1899) stated that he was ”satisfied by actual comparison of the specimens with one received from the Smithsonian Institution, that the species described by him as Mystaconurus heterolepis is the same as Goode and Bean’s Hymenocephalus cavernosus ”, and he believed ”that both these names will prove to be synonyms of Giglioli’s Hymenocephalus italicus from the Mediterranean”. After analysis of the specimens available to me, and in particular after investigation of the size of the orbit and the morphology of the otoliths, I conclude that H. heterolepis should be recognized as a valid species, in line with the recommendation made by Iwamoto (in Cohen et al., 1990).

Distribution ( Fig. 27 ). Hymenocephalus heterolepis appears to be geographically restricted to the sea around the Andaman Islands and the western coast of the Malay Peninsula.

Figures

FIGURE 24. Hymenocephalus heterolepis: A—CAS 50132, TL 93+ mm, lateral view of head. B–C—CAS 50132, TL 85+ mm, B—Lateral view of head, C—Dorsal view of head. D–E—Syntype, BMNH 1890.7.31.6, D—Lateral view of head, E—Dorsal view of head. F–G—CAS 50132, TL 85+ mm, F—Ventral view of head and trunk, G—detail view of posterior lens of ventral luminescent organ. H–M—Otoliths, CAS 50132, H—Anterior view, I, K–M—Inner faces, J—Ventral view.

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