Hymenocephalus semipellucidus Sazonov & Iwamoto, 1992

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 : 65-66

Hymenocephalus semipellucidus Sazonov & Iwamoto, 1992

Figs. 35D–H , 37

Hymenocephalus semipellucidus Sazonov & Iwamoto, 1992: 60 (type locality: Sala y Gomez Ridge, Prof. Shtokman cr. 18, sta. 2019).

Hymenocephalus semipellucidus: Iwamoto & Merrett, 1997: 523 (reference values only).

Material examined. 3 specimens ZMMGU P-18205, 135– 150 mm TL, 25°08’S, 99°25’W, 750– 800 m .

Diagnosis (after Sazonov & Iwamoto with additions). Pelvic fin rays 8; pectoral fin rays 15–19; gill rakers 15–20. Barbel short, 10–17% HL. Black blotch on dorsum long, with eroded outline. Orbit very large, 40–46% HL (43–50% HL along the longest diameter), slightly oblique. Snout rounded, very slightly protruding, 15–20% HL. Ventral striae extending to about ½ the distance from pelvic fin bases to periproct. Infraorbital width 9–11% HL. Otolith compressed with triangular shaped, not very high, pointed predorsal lobe, OL:OH = 0.8–0.9; colliculi fused, narrowed; pseudocolliculum very long, TCL:PCL = 1.25–1.35.

Comparison. Sazonov & Iwamoto (1992) distinguished H. semipellucidus from H. neglectissimus by a long black blotch on the dorsum (vs short and clear cut), shorter barbel, the higher number of pectoral rays (15–19 vs 13–16), the larger infraorbital width (9–11% HL vs 5–8% HL) and the slightly smaller orbit. It differs from H. aeger , H. megalops and H. torvus in the higher pectoral fin ray count (15–19 vs. 13–15, 14–16 and 12–14, respectively) and from H. aeger , H. striatissimus and H. torvus in the larger orbit (40–46% HL vs. 35–42% HL). An additional character to faultlessly distinguish H. semipellucidus from all species of the striatissimus Group is the outline of the otolith, with its less pronounced, triangular-shaped, pointed predorsal lobe.

Description. Head morphology (n = 1) ( Fig. 35D ): Snout short, slightly projecting, 15–20% HL, orbit diameter very large, 40–46% HL, 43–50% HL along the longest diameter, slightly obliquely oriented, interorbital width about 50–60% HW. Barbel, 10–17% HL (up to 22% HL according to Sazonov & Iwamoto). Head canals well developed, infraorbital width 9–11% HL, supraorbital canal with 4 segments, width 8% HL, supratemporal canal not identified, preopercular canal width 12% HL, postorbital-preopercular interspace 5% HL. Infranasal supporter short; infraorbital moderately long, narrow, 65% OD; preopercular supporter short, 5% HL, with straight rear margin.

Otolith morphology (n = 2) ( Fig. 35E–H ): Otolith large; OL:OH = 0.8–0.9; OH:OT = 3.2. Dorsal rim with rather short, broad, triangular shaped, pointed, smooth predorsal lobe, distally without marked indentation; posterior tip broadly rounded; ventral rim deep, regularly curved, smooth, deepest anterior of the middle; anterior rim high, subvertical vertical, slightly bent. Inner face slightly convex, with slightly supramedian sulcus. Colliculi completely fused, terminating far from anterior and posterior tips of otolith, dorsally reduced and rather narrow, leaving depressed sulcus space without collicular filling above; pseudocolliculum very long. TCL:PCL = 1.25–1.35. No dorsal depression; ventral furrow narrow, close to ventral rim of otolith.

Distribution ( Fig. 37 ). Hymenocephalus neglectissimus is only known from the Sala y Gomez Ridge.

Unidentifiable species

During the examination of the material, otoliths were extracted from two poorly preserved specimens, which seem

to represent two possibly undescribed species of the genus Hymenocephalus . The fish bodies are too poorly preserved to warrant any further description, let alone identification, but the otoliths are briefly described and figured below.

Figures

FIGURE 35. A–C: Hymenocephalus neglectissimus: A–C—ZMMGU-P 18221, A—Lateral view of head, B—Dorsal view of head, C—Schematic outline drawing of formalin eroded otolith. D–H: Hymenocephalus semipellucidus, ZMMGU-P 18205: D—Lateral view of head, E—Anterior view of otolith, F, H—Inner faces of otoliths, G—Ventral view of otolith.

FIGURE 37. Geographical distribution of Hymenocephalus aeger, H. megalops, H. striatissimus, H. torvus, H. grimaldii, H. neglectissimus, H. semipellucidus, H. sp. 1 and H.