Sharks

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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