Genus Hymenocephalus

Diagnosis: Branchiostegal rays 7. Head large, cavernous, covered by thin or membranous skin, tip of snout formed by thin, weak, laterally flattened mesial extension of the nasal bones. Mouth large, sub-terminal to almost terminal. Gill openings and outer gill slit wide, rakers numerous, usually more than 15 total on the inner series of first arch. First dorsal fin with a smooth (not serrated) spinous long second ray. Anus usually immediately before anal fin origin. Striae, consisting of fine parallel black lines over silvery ground on isthmus, shoulder girdle and chest. Light organ tubular with two lens-like windows, one before pelvic fin bases, the other round or oblate in outline and just anterior to the anus. Scales large, deciduous, with short fine spinules (obsolescent in some species). Retia mirablia and gas glands 2. (McMillan & Iwamoto 2014).