Decapod anatomy

[1][2] Each segment may possess one pair of appendages, although in various groups these may be reduced or missing.

In the Anomura (hermit crabs and related animals), the fifth pair of pereiopods is often hidden inside the branchial chamber, where they are used to clean the gills.

Pleopods (also called swimmerets) are primarily swimming legs, and are also used for brooding the eggs (except in prawns), catching food (then swept to the mouth), and can sometimes bear their own gills.

In some taxa, the first one or two pairs of pleopods are specialised in the males for fertilisation, and are referred to as the gonopods.

At the end of the pleon is the tail fan, comprising a pair of biramous uropods and the telson, which bears the anus.