Hymenocephalus striatulus Gilbert, 1905

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 : 45-46

Hymenocephalus striatulus Gilbert, 1905

Figs. 20A–G , 21

Hymenocephalus striatulus Gilbert, 1905: 665 (type locality: off south coast of Oahu , Hawaii).

Hymenocephalus striatulus: Sazonov & Iwamoto, 1992: 63 .

Material examined. 14 specimens; 1 specimen USNM 51611 (holotype), 114 mm TL, off southern coast of Oahu , 350–643 m ; 2 specimens USNM 406680 , 75 + and 120+ mm TL, 21°13’N, 157°43’W, 567 m ; 3 specimens (otoliths only) USNM 51683 , off Hawaii (no further details) ; 4 specimens ZMMGU P-17720, 63+ – 165 mm TL, 25°07’S, 99°26’W, 730–790 m ; 4 specimens ZMMGU P-22382, 24°59’S, 88°25’W, 550– 560 m .

Diagnosis. Pelvic fin rays 14–15; pectoral fin rays 15–18; snout projecting, 20–25% HL; barbel rudimentary or very short, 0–3% HL, not reaching vertical through anterior margin of orbit; orbit diameter moderate, 32–39% HL (mostly 33–38% HL); infraorbital width 10–12% HL; preopercular supporter moderately long, with obtuse angle at rear margin, 3–4% HL; gill rakers 25–29; ventral striae reaching to ½ from pelvic fin bases to periproct; otolith with moderately high predorsal lobe, colliculi separated, closely placed across collum, terminating far from anterior and posterior rims of otolith; OL:OH = 0.9–1.0; TCL:PCL = 1.7–2.0.

Comparison. Hymenocephalus striatulus is very similar to H. billsam with which it shares the presence of a small, sometimes only rudimentary barbel. For differences see H. billsam . The presence of a barbel, the slightly larger orbit size (33–38% HL vs 30–33% HL), and the higher pelvic fin ray count (14–15 vs 11–13) distinguishes H. striatulus from H. lethonemus and H. nascens .

Description. Head morphology (n = 2) ( Fig. 20A–B ): Snout projecting, long, 20–25% HL, orbit diameter 32–39% HL (mostly 33–38% HL according to Marshall & Iwamoto, 1973), interorbital width 50–60% HW. Barbel rudimentary or short, 0–3% HL. Head canals well developed, moderately large, infraorbital width 10–12% HL, supraorbital canal with 4–5 segments, width 14–16% HL, supratemporal canal not identified, preopercular canal width 12–14% HL, postorbital-preopercular interspace about 10% HL. Infranasal supporter rather large; infraorbital supporter short, expanding only beyond rear part of orbit, 40–50% OD; preopercular supporter moderately long, 3–4% HL, rear margin with indistinct bulge.

Otolith morphology (n = 9) ( Fig. 20C–G ): Otolith moderately large; OL:OH = 0.9–1.0; OH:OT = 3.0–3.5. Dorsal rim with a distinct, high and broad predorsal lobe, distally marked by indentation; posterior tip shifted above sulcus termination; ventral rim deep and regularly curved, deepest slightly anterior of the middle; anterior rim high; all rims more or less intensely crenulated. Inner face slightly convex, with median sulcus. Ostial and caudal colliculi very small, rather narrowly placed across collum, terminating far from anterior and posterior tips of otolith; pseudocolliculum moderately long. CCL:OCL = 0.7–1.1; TCL:PCL = 1.7–2.0. Dorsal depression small; ventral furrow rather indistinct, running at some distance from ventral rim of otolith.—Otoliths from larger specimens from USNM 406680 and ZMMGU P-17720 show a slightly more elongate shape in the range of OL:OH = 1.0–1.1, which I consider to reflect allometric ontogenetic growth. However, all these specimens are too poorly preserved to warrant figuring.

Discussion. When Sazonov & Iwamoto (1992) described H. striatulus from the Sala y Gomez Ridge in the SE Pacific, they noticed that those specimens only differ from the ones of the type locality, Hawaii, in the more distinct development of the barbel. They concluded that they “did not feel this single difference to be sufficient to recognize the species as distinct from H. striatulus ”. My investigations of the head morphology and the otoliths, the latter however hampered by poor preservation of the otoliths from the specimens from Sala y Gomez, do not add any further aspects and hence support their view of a single valid species, despite the considerable geographical distance between the two areas.

Distribution ( Fig. 21 ). Known from off Hawaii and Sala y Gomez.

Figures

FIGURE 20. Hymenocephalus striatulus: A–B—Holotype, USNM 51611, A—Lateral view of head, B—Dorsal view of head. C–G—Otoliths, USNM 51683, C—Anterior view, D, F, G—Inner faces, E—Ventral view.

FIGURE 21. Geographical distribution of Hymenocephalus billsam, H. lethonemus, H. nascens and H. striatulus.