Crabs can live for about a week when they are bought and put at home. Crab, belonging to the soft armour class and Decapoda, is a crustacean. Its body is protected by a hard shell and breathes by gills. In biological taxonomy, it is similar to shrimp, lobster and hermit crab. Crabs common crabs are Portunus, pelagic Portunus, green crab and Chinese mitten crab. Most species of crabs live in the sea or offshore areas, and some live in fresh water or land.
Most crabs are omnivorous. Some crabs are carnivorous. For example, the shuttle crab can catch fish, shrimp and molluscs. A few crabs, such as the femoral window crab, scrape or filter algae and organic debris.
A small number of crabs grow and reproduce completely in fresh water. They mostly inhabit under the stones of mountain streams. A few crabs, such as ground crabs, can adapt to land life, live in wet mud caves, and migrate to the sea during breeding. （PangXieZaiJiaNengHuoJiTian）