Hymenocephalus Giglioli, 1882

Iwamoto, Tomio, Nakayama, Naohide, Shao, Kwang-Tsao & Table, Hsuan-Ching Ho, 2015, Synopsis of the Grenadier Fishes (Gadiformes; Teleostei) of Taiwan, Proceedings of the California Academy of Sciences 62 (3), pp. 31-126 : 73

Genus Hymenocephalus Giglioli, 1882

DISTINGUISHING FEATURES.— Snout high, relatively rounded, median nasal process forming a weak snout tip (no horizontal platelike process mesially); paired nasal bone in broad contact along median line, without wide gap around nostril cartilage; head much deeper than wide; body relatively compressed; head mucous canals greatly expanded; head covering membranous and often transparent; light organ long, small lens on chest anterior to pelvic-fin bases connected by a black streak to round posterior lens immediately before anus; ventral striae well developed; fine black lines on gular membrane oriented perpendicular to median line, not netlike; inner GR-I, lower limb 12–16; spinous ray of 1D completely smooth; chin barbel present or absent.

REMARKS.— A genus of about 20 species, four of which are known from Taiwan. Most species do not exceed about 20 cm TL. The highly developed luminescent organ system consisting of a network of fine striations (“ventral striae”) on the cleithrum, chest, and belly regions is seen in gadiforms only in this genus, its closely related genera Hymenogadus and Spicomacrurus , and the monotypic genera Steindachneria Goode and Bean in Agassiz, 1888 and Lepidorhynchus Richardson, 1846 . The presence of two lens-like bodies of the light organ, one on the chest, the other immediately before the anus, is unique among the grenadiers to Hymenocephalus , Hymenogadus , and Spicomacrurus . The position of the lenses is similar to that of the ventral fossae of some species of Coelorinchus , but so far as we can determine, there are no comparable structures in that or other grenadiers. The delicate, paper-thin head bones and membranous head integument are usually damaged during capture, adding to the difficulties of identifying specimens.