The orders, families and genera of "Frilled and cow sharks"

This family is comprised of only one species. Frilled sharks possess 6 pairs of gill slits and have a slender, eel-like body with prominent keels on the abdomen. The first pair of gills is connected to each other across the throat, hence their name. They have a very short snout with a terminal mouth. Frilled sharks are wide-ranging but more patchily distributed. They prefer deeper waters of the outer continental shelves and upper slopes. A relatively rare species, exhibiting an ovoviviparous style of reproduction (aplacental viviparous) with a litter size of 8 to 12.

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).