Cow sharks represent a very ancient group of sharks. All species have either 6 or 7 pairs of gills. Compared to the closely related frill sharks (Chlamydoselachidae) that also possess 7 gill slits, the cow sharks first gill slits are not connected across the throat. Furthermore the mouth of cow sharks is not terminal but subterminal and they only possess one dorsal fin. Cow sharks show a world-wide distribution, preferably deeper water but some of them are more spottily distributed. Knowledge of their biology is only fragmentary but they seem to be very good swimmers since other sharks are among their preferred prey. All 4 species show an ovoviviparous style of reproduction (aplacental viviparity).
Typical species of the family of "Cow sharks":
Bigeye sixgill shark
No image of Bigeye sixgill shark found in the Shark Database