Hymenocephalus neglectissimus 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 : 64-65

Hymenocephalus neglectissimus Sazonov & Iwamoto, 1992

Figs. 35A–C , 37

Hymenocephalus neglectissimus Sazonov & Iwamoto, 1992: 56 (type locality: Sala y Gomez Ridge, Prof. Shtokman cr. 18, sta. 1964).

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

Material examined. 2 specimens ZMMGU P-18221, 105 and 112 mm TL, 23°33’S, 89°11’W, 563– 590 m .

Diagnosis (after Sazonov & Iwamoto with additions). Pelvic fin rays 8; pectoral fin rays 13–15; gill rakers 16–21. Barbel moderately long, 15–28% HL. Black blotch on dorsum short, with clear-cut outline. Orbit very large, 44–55% HL along the longest diameter, slightly oblique. Snout rounded, not protruding, 10–15% HL. Ventral striae extending to about ⅔ the distance from pelvic fin bases to periproct. Infraorbital width 5–8% HL. Otolith very compressed with broad, pointed predorsal lobe, OL:OH = 0.8.

Comparison. Hymenocephalus neglectissimus is a small species that is characterized by its large orbit size in combination with a long barbel and a narrow infraorbital width and narrow infraorbital supporter. Sazonov & Iwamoto used the sharp edged, short black blotch on the dorsum as a further character to distinguish H. neglectissimus from the co-occurring H. semipellucidus (long and eroded outline).

Description. Head morphology (n = 1) ( Fig. 35A–B ): snout short, rounded, not projecting, 10–15% HL, orbit diameter very large, 42–50% HL, 44–55% HL along the longest diameter, slightly obliquely oriented, interorbital width about 40–50% HW. Barbel moderately long, 15–20% HL (up to 28% HL according to Sazonov & Iwamoto), reaching slightly beyond vertical through anterior margin of orbit. Head canals well developed, infraorbital width 5–8% HL, supraorbital canal with 4 segments, width 6% HL, supratemporal canal indistinct, above segment 3 of supraorbital canal, preopercular canal width 10% HL, postorbital-preopercular interspace 4% HL. Infranasal supporter short; infraorbital very short and narrow, 25% OD; preopercular supporter short, 4% HL, with straight rear margin.

Otolith morphology (n = 1) ( Fig. 35C ): otolith large; OL:OH = 0.8. No sufficiently well preserved otolith was retrieved from any of the studied specimens. An outline could be reconstructed from one otolith, which has a very compressed shape and a broad, dorsally pointed predorsal lobe.

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

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.