Hymenogadus gracilis ( 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 : 25-26

Hymenogadus gracilis ( Gilbert & Hubbs, 1920)

Figs. 6A–I , 7

Hymenocephalus (Hymenogadus) gracilis Gilbert & Hubbs, 1920: 522 (type locality: Philippines, off southern Luzon ).

Hymenogadus gracilis: Okamura, 1970: 61 .

Hymenocephalus (Hymenogadus) gracilis: Marshall & Iwamoto, 1973: 602 ; Sazonov & Iwamoto, 1992: 55; Iwamoto & Merrett, 1997: 518.

Material examined. 12 specimens; 2 specimens ZMH 107658 , 53 and 65 mm TL, Great Meteor Bank , 30°00’N, 28°30’W, 300 m ; 8 specimens ZMH 111113 , 34°N, 07°W ; 1 specimen USNM 131873 , 27°22’N, 78°07’W, 0-618 m ; 1 specimen (otolith only), off Morocco, coll. IRSNB (courtesy D. Nolf) .

Diagnosis. Pelvic fin rays 8; pectoral fin rays 14–17; barbel long, 27–33% HL, reaching vertical through center of orbit; gill rakers 13–19; OL:OH = 1.25–1.55, increasing with size.

Comparison. Hymenogadus gracilis is very similar to H. tenuis , differing in the longer barbel (27–33% vs 12% HL), the higher number of pectoral fin rays (14–17 vs 12) and the higher number of gill rakers (13–19 vs 10).

Description. Head morphology (n = 2) ( Fig. 6A–D ): Head slender with projecting, broad, soft-tipped snout. No scale pockets visible on head, but present on nape. Snout length 17–20% HL, orbit diameter 35–38% HL, interorbital width 35–40% HW. Barbel 27–33% HL, reaching vertical through center of orbit or slightly further, but not to rear margin of orbit. Frontal, infraorbital, supraorbital and postorbital canals widened (infraorbital, supraorbital and postorbital widths 7–12% HL), covered by thin, but often well-preserved skin; preopercular and supratemporal canals fully skin covered and indistinct. Infranasal supporter small; infraorbital supporter narrow, extended and slightly expanded below and behind rear part of orbit, 30–50% OD; preopercular supporter broad, short (<3% HL). Few small pores visible in infraorbital skin.

Otolith morphology (n = 4) ( Figs. 6E–I ): Moderately thick, elongate otoliths with slightly convex inner and outer faces, the latter thickest opposite to ostium on inner face. OL:OH = 1.25–1.55, increasing with size; OH:OT = 3. Predorsal lobe expanded, somewhat posteriorly inclined, reaching to about mid-point of dorsal rim and there terminating in a sharp notch; ventral rim shallow; anterior tip rounded, posterior tip pointed. Sulcus median with narrow sulcus and narrow, ventrally indented collum. Colliculi large, reaching close to anterior and posterior rims of otolith, caudal colliculum longer than ostial colliculum (CCL:OCL = 1.6–2.1); pseudocolliculum indistinct, short; TCL:PCL = 7–10. Dorsal depression small, indistinct; ventral furrow thin, running very close to ventral rim of otolith.

Distribution. ( Fig. 7 ) Hymenogadus gracilis is a notably widespread species in the North Atlantic and the Indo West-Pacific from off East Africa to Japan and the Sala-y-Gomez Ridge in the southeastern Pacific at 300–450 m water depth according to Iwamoto & Merrett (1997), but excluding the Hawaiian Islands.

Figures

FIGURE 6. Heads and otoliths of the species of Hymenogadus: A–I—Hymenogadus gracilis, A–D—ZMH 111113, A—Dorsal view of head, B—Ventral view of head and trunk, C–D—Lateral views of head, E—Inner face of otolith, coll. Schwarzhans (leg. IRSNB), F–H—USNM 131873, F—Anterior view of otolith, G—Inner face of otolith, H—Ventral view of otolith, I—ZMH 107658, inner face of otolith. J–L—Hymenogadus tenuis, holotype, J—Lateral view of head, K—Dorsal view of head, L—Radiograph of head depicting otolith.

FIGURE 7. Geographical distribution of the species of Hymenogadus.