Largetooth cookiecutter shark

The largetooth cookiecutter shark, Isistius plutodus, is a sleeper shark of the family Dalatiidae found in the western Atlantic Ocean off Alabama and the Gulf of Mexico including Brazil, and the northwest Pacific Ocean off Okinawa, at depths of between 880 and 6,440 m.  Its length is up to 42 cm.

The largetooth cookiecutter shark has an extremely short snout, and anteriorly positioned eyes which allows for binocular vision. It has no collar marking around the throat, a small asymmetrical caudal fin with a short ventral lobe less than half the length of the dorsal caudal margin, bigger mouth and gigantic lower teeth (proportionately the largest in any living shark) in 19 rows (upper teeth = 29 rows). The pectoral fins are rounded, with the pelvic fins smaller than the dorsal fins. As with the other member of the genus Isistius, it has a characteristic small cigar-shaped body with two small close-set spineless dorsal fins far posterior on back, no anal fin, and huge, triangular-cusped teeth. It has a large oily liver which helps it to become neutrally buoyant. Its powerful jaws, big mouth and enormous lower teeth enable it to bite off large portion of its prey in one sweeping motion.

Reproduction is ovoviviparous.