Back bluish, turning to deep purple or almost black on head. Scaleless area with pattern of 15 or more fairly broad, nearly vertical dark bars. Belly white. Pectoral and pelvic fins purple, their inner sides black. Body robust, elongate and rounded. Teeth small and conical, in a single series. Pectoral fins short, not reaching vertical line from anterior margin of scaleless area above corselet. A large, single-pointed flap (interpelvic process) between pelvic fins. Body naked except for corselet, which is well developed in its posterior part 9 more than 6 scales wide under second dorsal-fin origin). A strong central keel on each side of caudal-fin base between 2 smaller keels (Ref 9684).