internal organs, covered by a shell called the carapace, and a muscular tail section that is usually folded under the body. Many crustaceans have powerful pincers that they use to capture and break up their prey, and to signal to other s of their species. Crustaceans live in the sea and also freshwater habitats. Many small crustaceans feed on plankton. These crustaceans thus form an important link between the small food-producing organisms and the larger animals in the aquatic food chain.