Blue Crab info.

Blue king crab, like all king crabs are decapod or “ten-legged” crustaceans that have "tails," or abdomens, that are distinctive, being fan-shaped and tucked underneath the rear of the shell. They also have five pairs of legs; the first bears their claws or pincers, the right claw is usually the largest on the adults, the next three pairs are their walking legs, and the fifth pair of legs are small and normally tucked underneath the rear portion of their carapace (the shell covering their back). These specialized legs are used by adult females to clean their embryos (fertilized eggs) and the male uses them to transfer sperm to the female during mating.

-Alaskan Department of Fish & Game