The body of a decapod crustacean is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess one pair of appendages, although in various groups these may be reduced or missing. They are, from head to tail:

Cephalothorax

Head

1. antennules
2. antennae
3. mandibles
4. first maxillae
5. second maxillae

The head also bears the (usually stalked) compound eyes.

Thorax

1. first maxillipeds
2. second maxillipeds
3. third maxillipeds
4. first pereiopods
5. second pereiopods
6. third pereiopods
7. fourth pereiopods
8. fifth pereiopods

Maxillipeds are legs modified to function as mounthparts. Particularly in the less advanced decapods, these can be very similar to the pereiopods. Pereiopods are primarily walking legs and are also used for gathering food. Those pereiopods which are armed with a claw (chela) are sometimes referred to as chelipeds. The pereiopods which bear the sexual organs, which are the third pereiopod in the female and the fifth pereiopod in the male, may be referred as as gonopods. Each appendage from the second maxilla to the fifth pereiopod also bears a gill. In the Anomala (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. The cephalothorax is covered by a carapace which protects the internal organs and the gills; the section of the carapace that projects in front of the eyes is called the rostrum.

Abdomen / Pleon

1. first pleopods
2. second pleopods
3. third pleopods
4. fourth pleopods
5. fifth pleopods
6. uropods

Pleopods are primarily swimming legs, and are also used for brooding the eggs (except in prawns). At the end of the abdomen, a pair of biramous uropods are used for steering, and in the "caridoid escape reaction", along with the telson, which bears the anus. In crabs and some other carcinised decapods, the abdomen is folded under the cephalothorax.