The body of a decapod crustacean, such as a crab, lobster, or prawn (shrimp), is made up of twenty body segments. They are grouped into two main body parts, the cephalothorax and the abdomen. Each segment may have one pair of appendages. In some groups these may be reduced or missing. On average, crayfish grow to in length, but some grow larger. Walking legs have a small claw at the end.