Pectoral fins moderately falcate; mouth subterminal; spiracles long, slit-like and dorsal to the plane of the pectoral fins; densely cover most of the body surfaces; tail whip-like and very long, subequal to or exceeding disc width when undamaged; a short serrated caudal spine usually present behind dorsal fin. Body colour bluish black above with 2 crescentic white patches on shoulders, most obvious in embryos and juveniles, fading in adults; white ventrally, sometimes with dark patches in adults.