Hermit crabs are decapod crustaceans. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab. Typical for the hermit crabs is their soft, unprotected abdomens which they hide inside an empty shell. As they grow, they have to replace the shell with larger ones. Some species have a twisted abdomen, with a shape adapted to fit into a particular kind of shell. Some hermit crabs do not use a shell at all, but use an anemone with stinging threads to protect themselves. The order Decapoda includes the following: crab, lobster, or shrimp, characteristically having ten legs, each joined to a segment of the thorax. It can also be a cephalopod mollusk, such as a squid or cuttlefish, having ten armlike tentacles.