The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these may be reduced or missing.
Cephalothorax
Head
- antennules
- antennae
- mandibles
- first maxillae
- second maxillae
The head also bears the (usually stalked) compound eyes. The distal portion of a mandible or maxilla which has a sensory function is known as a palp.
Thorax / pereon
- first maxillipeds
- second maxillipeds
- third maxillipeds
- first pereiopods
- second pereiopods
- third pereiopods
- fourth pereiopods
- fifth pereiopods
Maxillipeds are appendages modified to function as mouthparts. 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. They are also the ten legs from which decapods take their name.