Cow sharks are little known because they spend most of their time in the deep.

Bluntnose Sixgill Shark (Hexanchus griseus). Illustration: R. Aidan Martin

Cow sharks are little known because they spend most of their lives in deep, cold oceans beyond the reach of divers. However, there are times during the year when some species spend time in shallow waters to feed and give birth.

Cow sharks are unusual in that they have six, and in some species, seven pairs of gills. They have wide heads, small eyes, and heavily-built body.