Frill and cow shark information and info on the Hexanchiformes also known as Frill and cow sharks
Hexanchiformes is the order consisting of the most primitive types of sharks, and numbering just five existing species. Fossil sharks that were apparently very similar to modern seven gill species are known from Jurassic specimens.
Frill and cow 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.