An exoskeleton (from Greek έξω, éxō "outer" and σκελετός, skeletos "skeleton") is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton (endoskeleton) of, for example, a human. In usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers and cockroaches, and crustaceans such as crabs and lobsters. The shells of certain sponges and the various groups of shelled mollusks, including those of snails, clams, tusk shells, chitons and nautilus, are also exoskeletons.