蟹 (crab) is a type of crustacean found in oceans, freshwater, and on land. They have a hard shell, ten limbs, and are known for their sideways walking. Crabs belong to the order Decapoda, which means "ten-footed," and they play an important role in marine ecosystems as scavengers and predators. There are many species of crabs, including the popular blue crab and king crab. Crabs are also a significant source of food for humans and are enjoyed in various cuisines around the world. Their unique appearance and behavior make them a subject of interest in both science and culture.