Hymenocephalus aeger Gilbert & Hubbs, 1920

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 : 58-59

Hymenocephalus aeger Gilbert & Hubbs, 1920

Figs. 30A–G, 37

Hymenocephalus striatissimus aeger Gilbert & Hubbs, 1920: 531 (type locality: 00°15’N, 127°24’E).

Hymenocephalus striatissimus aeger: Iwamoto & Williams, 1999: 178 .

Material examined. 11 specimens; 1 specimen MNHN 2006-0159 , 07°44’S, 156°29’E, 518–527 m ; 1 specimen MNHN 2006-0218 , 08°09’S, 157°01’E, 460–487 m ; 3 specimens MNHN 2006-0556 , 91 + – 140 mm TL, 08°16’S, 160°04’E, 430 m ; 1 specimen WAM P.30578-002, 121 mm TL, 17°57’S, 118°17’E ; 1 specimen ZMUC P375844 , 84 + mm TL, Kai Islands ; 1 specimen ZMUC P 375854, 127 mm TL, Kai Islands ; 1 specimen ZMUC P375856 , 91 + mm TL, Kai Islands ; 1 specimen ZMUC P 375857, 126 mm TL, Kai Islands ; 1 specimen ZMUC unregistered, 05°46’S, 132°52’E .

Diagnosis. Pelvic fin rays 8; pectoral fin rays 13–15; gill rakers 19–23. Barbel long, 20–25% HL, reaching beyond a vertical through anterior rim of orbit. Orbit 35–40% HL. Snout obtuse, slightly protruding, 15–18% HL. Ventral striae extending to about ⅔ the distance from pelvic fin bases to periproct. Infraorbital supporter long, 70–90% OD. Otolith compressed, OL:OH = 0.9–1.0; colliculi fused; pseudocolliculum long, TCL:PCL = 1.25–1.45.

Comparison. Hymenocephalus aeger was established by Gilbert & Hubbs (1920) as a subspecies of H. striatissimus on the basis of a longer barbel and a smaller eye. The difference in the eye (orbit) size was not verified from the specimens examined, but the longer barbel is quite distinct. In addition, the otoliths are slightly less compressed than those of the other species of the striatissimus Group (OL:OH = 0.9–1.0 vs 0.75–0.9). This subtle difference in otolith proportions further supports the recognition of a separate taxonomic entity.

Description. Head morphology (n = 2) ( Fig. 30A): Snout rather short and obtuse, only slightly projecting, 15–18% HL, orbit diameter large, 35–40% HL, interorbital width 60–70% HW. Barbel long, 20–25% HL, reaching slightly beyond a vertical through anterior rim of orbit. Head canals well developed, infraorbital width 11–14% HL, supraorbital canal with 4 to 5 segments, width 10–15% HL, supratemporal canal rarely identifiable, above segment 3 or 4 of supraorbital canal, preopercular canal width 12–16% HL, postorbital-preopercular interspace 4–7% HL. Infranasal supporter moderately 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 = 10) ( Fig. 30B–H): Otolith large; OL:OH = 0.9–1.0; OH:OT = 3.5. Dorsal rim with very large, moderately broad, smooth predorsal lobe, distally marked by small concavity, inclining to posterior tip; posterior tip slightly expanded, positioned 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. Colliculi completely fused, terminating far from anterior and posterior tips of otolith; pseudocolliculum very long. TCL:PCL = 1.25–1.45. Dorsal depression small, indistinct; ventral furrow distinct, close to ventral rim.

Discussion. Gilbert & Hubbs (1920) studied a large number of specimens of the three nominal subspecies of H. striatissimus , and recorded that they found intergrades between H. striatissimus aeger and H. s. torvus along the Tawi Tawi Archipelago of the Philippines, which led them to establish this form as a subspecies of H. striatissimus . I was unable to verify their observation of intergrades, but found a specimen from off the nearby Jolo Island in the collection of ZMUC (P375860), which I consider as H. striatissimus ( Fig. 32B–C). Since otoliths seem to present a further character helpful to identify H. s. aeger , I now tentatively propose full species rank for H. aeger , subject however to verification of a more detailed and possibly statistical assessment of this difficult species group.

Distribution ( Fig. 37). Specimens studied and considered valid for H. aeger are from off NW-Australia, off southern New Guinea and off the Solomon Islands.