Distribution: Atlantic, Indian, and Pacific Oceans. Most species are deepwater inhabitants of the outer continental shelves and upper continental slopes down to at least 1875 m depth. Gill openings 6 in Hexanchus, 7 in Heptranchias and Notorynchus. Margin of first gill discontinuous across throat. Mouth subterminal with large, bladelike, comb-shaped teeth in lower jaw. One dorsal fin. Caudal fin with strong subterminal notch. Cow sharks are ovoviviparous and lack a yolk-sac placenta. They feed on relatively large marine organisms, including other sharks, rays, bony fish, crustacean and carrion. Species range in size from 140 to 480 cm. hexa- (gr.) = six
Note: Families with unknown counts of dorsal or anal spines are also included