Physical 

The Blue Crab carapace (hard upper shell) reaches up to 9 inches point to point, with nine marginal teeth around the edges; the ninth is the point of measurement. The appendages are bright blue when they are older, paler as juveniles. The two paddle-shaped back appendages are called swimmerets; they help the crab swim quickly.

Habitat

C. sapidus range from Cape Cod to Uruguay, and live in estuaries, bays, and the open ocean, varying in salinities. They take shelter in eel grass beds and other structures for protection while breeding and molting.

Feeding 

Blue Crabs are scavengers of the sea floor. They are omnivores that eat anything they find, such as oysters, mussels, clams, smaller crustaceans, freshly dead fish, and plant and animal detritus.