Astacidea

Astacidea is an infraorder of decapod crustaceans that groups the true lobsters, the freshwater crayfish and their close relatives, while leaving out the spiny lobsters, which belong elsewhere in the decapod tree. Its members are told apart from most other decapods by claws (chelae) on each of the first three pairs of walking legs, the first pair being far larger than the other two; the last two pairs are simple, apart from the deep-sea genus Thaumastocheles, whose fifth leg may carry a minute pincer. The infraorder is found in oceans and fresh water around the world except mainland Africa and parts of Asia. It sits within the walking decapods (Reptantia) and is the sister clade of the small deep-water infraorder Polychelida. Four living superfamilies are recognised: two of crayfish (Astacoidea and Parastacoidea), one of true lobsters (Nephropoidea) and one of reef lobsters (the genus Enoplometopus), plus a number of fossil groups. As of 2009 it held 782 recognised species, over 400 of them in the crayfish family Cambaridae.