六鳃鲨目是板鳃类的一目，有6至7个鳃孔（一般鲨鱼只有五个），一个背鳍，共有两科：

• 六鳃鲨科(Hexanchidae)
• 皱鳃鲨科(Chlamydoselachidae)

六鳃鲨科体形类似鲨，但细长，下颌短，齿异形。

皱鳃鲨科鱼体形长，类似鳗鱼，背鳍、腹鳍、臀鳍都在身体后部，互相靠近，第一鳃孔两侧相通。

六鳃鲨目一般在海底层栖息，以鱼和甲壳类动物为食，卵胎生。

Hexanchiformes is the order consisting of the most primitive types of sharks, and numbering just six extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens.

Hexanchiform sharks have only one dorsal fin, either six or seven gill slits, and no nictitating membrane in the eyes.