What are the major structures in a crustacean?

Answer 1

I am going to assume you are talking about decapod crustaceans, which is the kind most people eat. You can imagine a lobster as I describe the parts, but the description applies generally to all decapods, even crabs. The animal is covered by a chitinous exoskeleton. The shell that makes up the head is called a carapace, and it covers both the animal's head and thorax (similar to your torso). The head and thorax in a lobster have been fused together to form a cephalothorax. The part most people call a tail is actually the abdomen of the animal. Now I'll describe the main appendages on the animal going from front to back. In front, there are 10 walking legs (5 on each side), called pereiopods (pereio = thorax, pod = leg or foot). Usually, at least the first pair are modified at the tips to form chelae(claws). These are always attached to the cephalothorax. There are also appendages attached to the bottom of the abdomen, called pleopods (pleo = abdomen, pod = leg or foot). At the very end of the tail, there are additional flattened appendages which make up the tail fan. The flattened portion are called uropods (uro = tail). The center piece, flat in lobsters, a sharpened tip in shrimp, is called the telson. Crabs are constructed more or less the same way except the abdomen is greatly reduced and folded under the cephalothorax (check it out next time you are eating a crab!).