Hymenocephalus nascens, 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 : 43-45

Hymenocephalus nascens Jordan & Hubbs, 1920

Figs. 19A–P , 21

Hymenocephalus nascens Jordan & Hubbs , 1920: 535 (type locality: 04°10’N, 118°37’E) .

Hymenocephalus nascens: Iwamoto & Merrett, 1997: 523 ; Iwamoto & Williams, 1999: 177; Merrett & Iwamoto 2000: 759; Iwamoto & McCosker, 2014: 281.

Hymenocephalus lethonemus: Weber, 1913: 167 .

Material examined. 24 specimens; 1 specimen AMS I.17813-009, 121+ mm TL, 22°05’S, 165°50’E, 880 m; 4 specimens BSKU 98184-98187 , 99– 125 mm TL, 05°56’S, 119°29’E, 630–657 m ; 3 specimens (otoliths only) MNHN 1995-0873 , 18°46’S, 168°55’E, 641–649 m ; 3 specimens (otoliths only) MNHN 2008-2442 , 16°16’S, 167°18’E, 630–690 m ; 2 specimens (otoliths only) MNHN 2011-0216 , 16°16’S, 167°18’E, 630–690 m ; 3 specimens (otoliths only) USNM 99451 , 04°06’N, 118°47’E ; 1 specimen WAM P.31799-003, 135 mm TL, 21°39’S, 113°51’E ; 2 specimens WAM P.32344-001, 47+ –101+ mm TL, 21°29’S, 113°58’E ; 1 specimen ZMUC 375859 , 08°36’S, 114°34’E, 300 m ; 1 specimen ZMUC 375861 , off Zamboango , Philippines .

Diagnosis. Pelvic fin rays 12–13, rarely 11 on one side only; pectoral fin rays 13–16; snout projecting, 20–26% HL; barbel absent; orbit diameter moderate, 30–33% HL; infraorbital width 11–16% HL; preopercular supporter moderately long, with obtuse angle at rear margin, 4–9% HL; gill rakers 22–27; ventral striae reaching to ½ distance from pelvic fin bases to periproct; otolith with moderately high predorsal lobe, colliculi separated, narrowly placed across collum with a tendency to joining in large specimens, terminating at some distance from anterior and posterior rims of otolith; OL:OH = 1.1–1.2; TCL:PCL = 1.8–2.4.

Comparison. Hymenocephalus nascens is very similar to H. lethonemus (see above). Gilbert & Hubbs (1920) mentioned a single difference between the two species being the pelvic fin ray count with dominantly 12–13 in H. nascens and 11 in H. lethonemus , however, with a number of specimens in both species exhibiting 11 fin rays on one fin and 12 on the other. Since otoliths also exhibit some subtle difference in proportions and collum width (see above), I am tentatively regarding both nominal species valid subject to later investigations.

Description. Head morphology (n = 5) ( Fig. 19A–F, N ): Snout projecting, long, 20–26% HL, orbit diameter 30–33% HL, interorbital width 50–60% HW. Barbel absent. Head canals well developed, moderately large, infraorbital width 11–16% HL, supraorbital canal with 5 segments, width 10–16% HL, supratemporal canal narrow, above segment 4 of supraorbital canal, preopercular canal width 9–15% HL, postorbital-preopercular interspace 4–10% HL. Infranasal supporter moderately large; infraorbital supporter short, expanding only beyond rear part of orbit, 30–50% OD; preopercular supporter moderately long, 4–9% HL, rear margin with obtuse angle. Hymenocephalus nascens was represented in collections by a relatively large number of well-preserved specimens from a variety of locations. This allowed mapping a larger degree the variability in morphometric characters of the head than was possible with most other species investigated.

Otolith morphology (n = 13) ( Fig. 19G–M, O–P ): Otolith moderately large; OL:OH = 1.1–1.2; OH:OT = 3.0. Dorsal rim with a distinct, narrow, slightly forward inclined predorsal lobe with rounded tip, distally marked by incision; posterior tip shifted above sulcus termination; ventral rim 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 moderately small, narrowly placed across collum, terminating at some distance from anterior and posterior tips of otolith; pseudocolliculum moderately long. CCL:OCL = 0.7–1.1; TCL:PCL = 1.8–2.4. Dorsal depression small; ventral furrow distinct, close to ventral rim. Otoliths of the largest specimen available ( Fig. 19O–P ) show a reduced height of the predorsal lobe and an incipient joining of the colliculi. All other characters including detailed head morphology ( Fig. 19N ) are within the range of H. nascens . It is therefore assumed that these changes in otolith morphology reflect late-stage ontogenetic changes, something which otherwise has not been observed much in Hymenocephalus otoliths.

Distribution ( Fig. 21 ). Hymenocephalus nascens is common and widespread in the West Pacific, from the Philippines off Luzon to the Flores and Halmahera Seas, around the island chains of the Solomons, Vanuatu, Fiji, Wallis and Futuna, New Caledonia and Norfolk Ridge, Chesterfield Plateau and Lord Howe Rise, and the eastern coast of Australia off New South Wales and Western Australia from the Dampier Archipelago to off Northwest Cape.

Figures

FIGURE 19. Hymenocephalus nascens: A–B—MNHN 1995-0873, A—Lateral view of head, B—Dorsal view of head. C—BSKU 098184, lateral view of head. D–E—WAM P.32344-001, D—Lateral view of head, E—Dorsal view of head. F—AMS I.17813-009, lateral view of head. G–M, O–P—Otoliths, G–I, L–M, P—Inner faces, J—Anterior view, K, O—Ventral views, G—WAM P.32344-001, H—BSKU 98184, I–K—BSKU 98187, L–M—USNM 99451, O–P—WAM P.31799-003. N—WAM P.31799-003, lateral view of head.

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