Though several groups of crustaceans are known as lobsters, the clawed lobsters are most often associated with the name. Clawed lobsters are not closely related to spiny lobsters or slipper lobsters, which have no claws (chelae), or squat lobsters. The closest relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish.
Lobsters are invertebrates with a hard protective exoskeleton. Like most arthropods, lobsters must molt in order to grow, which leaves them vulnerable. During the molting process, several species change color. Lobsters have 10 walking legs; the front three pairs bear claws, the first of which are larger than the others. Although, like most other arthropods, lobsters are largely bilaterally symmetrical, they often possess unequal, specialized claws, like the king crab.