Crabs and shrimp belong to the same arthropod phylum, Crustacea, decapods. The body of the bladder crab consists of the head, thorax and abdomen, the head is often fused with the thorax into a cephalothorax. The organs of action are the appendages. The body is protected by a butylated shell, and most live in the water, breathing through gills or on the surface of the skin. The abdomen of the crab is retracted below the thorax (narrow in males and wide in females) and is often called the umbilicus. Crustaceans are a large family of arthropods, with more than 30,000 species worldwide, most of which live in the oceans, from the intertidal zone to the deep sea. There are many different kinds of crabs, many different forms, and there are more than 600 kinds of crabs found, most of which are edible.