Hexanchiformes

Hexanchiformes is the order consisting of the most primitive types of sharks, and numbering just a handful of species.

Hexanchiform sharks have only one dorsal fin[?], either six or seven gill slits[?], and no nictitating membrane[?] in the eyes.

The frilled shark Chlamydoselachus anguineus is very different from the cow sharks, and it has been proposed that it be moved to its own order Chlamydoselachiformes.