DECAPOD ANATOMY

(Redirected from Pleopod)






The body of a decapod crustacean, such as a crab, lobster, or prawn, 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:

Contents

Cephalothorax

Head

Thorax / Pereon

Abdomen / Pleon

Cephalothorax

Head

#antennules
#antennae
#mandibles
#first maxillae
#second maxillae
The head also bears the (usually stalked) compound eyes.

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. Those pereiopods which are armed with a claw (''chela'') are sometimes referred to as 'chelipeds'. The pereiopods bear the sexual organs, which are the third pereiopod in the female and the fifth pereiopod in the male. Each appendage from the second maxilla to the fifth pereiopod also bears a gill. 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. 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

#first pleopods
#second pleopods
#third pleopods
#fourth pleopods
#fifth pleopods
#uropods
'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. Together, they are used for steering while swimming, and in the caridoid escape reaction.
In crabs and some other carcinised decapods, the abdomen is folded under the cephalothorax.