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.
Hexanchiformes Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Chondrichthyes Order: Hexanchiformes Families
Chlamydoselachidae (frilled shark)
Hexanchidae[?] (cow sharks)