Hymenocephalus billsam Marshall & Iwamoto, 1973

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 : 41-42

Hymenocephalus billsam Marshall & Iwamoto, 1973

Figs. 17A–H , 21

Hymenocephalus billsam Marshall & Iwamoto, 1973: 610 (type locality: off Puerto Rico, 17°49’N, 66°11’W). Hymenocephalus billsam: Prokofiev & Kukuiev, 2009: 165 .

Hymenocephalus billsamorum (name change): Iwamoto in Cohen et al., 1990: 230.

Material examined. 21 specimens; 7 specimens MCZ 43045, 85 + – 114 mm TL, 12°26’N, 82°24’W ; 6 specimens MCZ 43047, 85 + – 122 mm TL, 10°10’N, 59°54’W, 640 m ; 5 specimens MCZ 43048, 116– 138 mm TL, 16°58’N, 87°53’W, 457–731 m ; 1 specimen USNM 198181 (holotype), 140 mm TL, 17° 49°N, 66°11’W, 805 m ; 1 specimen (otolith only) USNM 209262 (paratype #4), 15°38’N, 61°12’W, 585 m ; 1 specimen (otolith only) USNM (not catalogued), R / V Oregon St. 3561 .

Diagnosis. Pelvic fin rays 12–14, mostly 13–14; pectoral fin rays 14–17; snout projecting, 20–25% HL; barbel short, 4–5% HL, not reaching vertical through anterior margin of orbit; orbit diameter moderate, 28–35% HL; infraorbital width 12–15% HL; preopercular supporter moderately long, with angle at rear margin, 5–6% HL; gill rakers 23–28; ventral striae reaching to ½ to ⅔ distance from pelvic fin bases to periproct; otolith with moderately high predorsal lobe, colliculi separated, closely placed across collum, terminating at some distance from anterior and posterior rims of otolith; OL:OH = 1.05; TCL:PCL = 2.6–2.8.

Comparison. Hymenocephalus billsam is very similar to H. striatulus with which it shares the presence of a small barbel. It differs in the smaller number of fin rays (12–14 vs 14–15) and somewhat smaller orbit (28–35% HL, mostly smaller 33% HL vs 32–39% HL, mostly 33–38% HL), both apparently with a certain degree of overlap. Otoliths provide for further characters for distinction, with H. billsam showing a more elongate otolith with a relatively short pseudocolliculum compared to H. striatulus (OL:OH = 1.05 vs 0.95–1.0 and TCL:PCL = 2.6–2.8 vs 1.7–2.0). From the other two species in the striatulus group, it differs in the presence of a small barbel (vs no barbel) and from H. lethonemus , also in the higher number of pelvic fin rays (mostly 13–14 vs mostly 11).

Description. Head morphology (n = 3) ( Fig. 17A–D ): Snout projecting, long, 20–25% HL, orbit diameter 28–35% HL (mostly 28–33% HL according to Marshall & Iwamoto, 1973), interorbital width 50–60% HW. Barbel short, 4–5% HL, not reaching vertical through anterior margin of orbit. Head canals well developed, moderately large, infraorbital width 12–15% HL, supraorbital canal with 5 segments, width 12–15% HL, supratemporal canal narrow, above segment 3 of supraorbital canal, preopercular canal width 10–12% HL, postorbital-preopercular interspace very variable, 5–11% HL. Infranasal supporter small; infraorbital supporter short, expanding only beyond rear part of orbit, 20–50% OD; preopercular supporter moderately long, 5–6% HL, rear margin with bulge or obtuse angle, a feature typical for the striatulus group and first recognized in H. billsam by Marshall & Iwamoto (1973).

Otolith morphology (n = 6) ( Fig. 17E–H ): Otolith large; OL:OH = 1.05; OH:OT = 3.0. Dorsal rim with a distinct predorsal lobe, postdorsally somewhat undulating and regularly inclined towards rounded posterior tip; posterior tip shifted above sulcus termination; ventral rim regularly curved, smooth, deepest anterior of the middle; anterior rim high, nearly vertical. Inner face slightly convex, with median sulcus. Ostial and caudal colliculi small, rather narrowly placed across collum, terminating at some distance from anterior and posterior tips of otolith; pseudocolliculum short. CCL:OCL = 0.9–1.2; TCL:PCL = 2.6–2.8. Dorsal depression small; ventral furrow distinct, close to ventral rim, anteriorly and posteriorly turning upwards to the sulcus.

Distribution ( Fig. 21 ). Hymenocephalus billsam is common and rather widely distributed in the Caribbean and along the east coast of the USA to off North Carolina. Also known from apparently disjunct distribution off southern Brazil from 11°– 24°S and over the Rio Grande Rise.

Isolated otoliths of H. billsam have also been obtained from sea bottom dredges off southern Azores by Schwarzhans (2013). In the same paper, other otoliths dredged from off Guinea and Ghana were also tentatively associated as H. aff. billsam , but these are less well-preserved and differ somewhat in their more compressed shape, a narrow collum and long pseudocolliculum. They could potentially represent another species not yet recorded from the Atlantic. All these dredged samples are supposed to be of Holocene age and indicate that H. billsam was distributed across a larger area in the recent past.

Figures

FIGURE 17. Hymenocephalus billsam: A, D—Holotype, USNM 198181, A—Lateral view of head, D—Dorsal view of head. B–C—MCZ 43048, B—Lateral view of head, C—Dorsal view of head. E–G—Paratype, USNM 209262, E—Anterior view of otolith, F—Inner face of otolith, G—Ventral view of otolith. H—MCZ 43048, inner face of otolith.

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