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Sharks constitute the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It is currently thought that the sharks form a polyphyletic group: in particular, some sharks are more closely related to rays than they are to some other sharks.
Sharks are split into eight orders:
- Carcharhiniformes: ground sharks, the largest order of sharks, including requiem sharks, catsharks, swellsharks, houndsharks, weasel sharks and hammerheads
- Heterodontiformes: bullhead sharks
- Hexanchiformes: cow sharks and frilled sharks
- Lamniformes: mackerel sharks, including thresher sharks
- Orectolobiformes: carpetsharks
- Pristiophoriformes: sawsharks
- Squaliformes: bramble sharks, dogfish, sleeper sharks and lanternsharks
- Squatiniformes: angelsharks