Low keels on caudal peduncle. Gill-slits very small.
Pectoral fins small.
Posterior margins of all fins lighter and rather transluscent. To about 50cm. Size at birth unknown. Very rare but essentially unknown regionally. Cookiecutters are unique sharks, having gained notoriety as facultative ectoparisites upon a wide variety of large marine animals, including cetaceans, northern elephant seals, and other pinnipeds, tunas, billfish and even the equally-mysterious megamouth shark.