Lobsters

Lobsters are large crustaceans in the order Decapoda, which also includes about 10,000 species of crayfish, crabs, and shrimps. Decapods are characterized by having their carapace fused with their thoracic segments to form a gill chamber above where the legs join the body, and the first three of their eight pairs of thoracic legs are modified into grasping, clawlike structures known as maxillipeds.

There are two major groups of lobsters: the typical lobsters, in the infraorder Astacidea, and the spiny lobsters, in the infraorder Palinura.

The true lobsters, and the closely related crayfish, have their three pairs of maxillipeds developed as chelae, or large pincer-like claws used for catching and handling food, and for defense. The first pair of claws is especially large. These animals also have well-developed uropods, a paired appendage that arises from the last segment of the body and forms a major part of the tail fan. The spiny lobsters are not chelate (that is, they do not have large foreclaws), and their third maxilliped resembles a leg.