Diagnosis: body naked, elongated, cylindrical in front and strongly compressed back; caudal part of body making less than one third of the total length and ending in a blunt point; no paired fins; dorsal and anal fins reduced to a skin fold, rayless, meeting the caudal fin; eyes small, overlaid with skin, situated at the head forward; mouth large with well developed lips; conical teeth to the jaws and the palate; gill opening reduced to a medio-ventral transversal slit; branchiostegal membrane free from isthmus; 4 branchial arches with well developed branchiae; lateral line present; vertebral count: 80 abdominal and 50 caudal (Ref. 57291).

Colouration: adults are dark-coloured, nearly black, juveniles are clearer (Ref. 57291).