Astacidea

The Astacidea are a group of decapod crustaceans including lobsters, crayfish, and their close relatives. The infraorder Astacidea comprises five extant superfamilies, two of crayfish (Astacoidea and Parastacoidea), one of true lobsters (Nephropoidea), one of reef lobsters (the genus Enoplometopus), and a number of fossil taxa. As of 2009, the group contains 782 recognised species, over 400 of which are in the crayfish family Cambaridae. The members of the infraorder Glypheidea (containing numerous fossils and the two extant species Neoglyphea inopinata and Laurentaeglyphea neocaledonica) were formerly included here. The Astacidea are distinguished from most other decapods by the presence of chelae (claws) on each of the first three pairs of pereiopods (walking legs), the first of which is much larger than the remaining two pairs. The last two pairs of pereiopods are simple (without claws), except in Thaumastocheles, where the fifth pereiopod may have 'a minute pincer'. Members of the infraorder Astacidea are found throughout the world – both in the oceans and in fresh water – except for mainland Africa and parts of Asia.