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.