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.
Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton.
Exoskeletons are hard, external structures that support and protect an animal's body. Exoskeletons provide protection from predators but limit the growth of the animal. Many animals enlarge or shed their exoskeletons as they grow.
Insects are an example of animals that have an exoskeleton. They do not have internal bones, and their muscles are attached to the exoskeleton. When a muscle contracts, it pulls on the exoskeleton and causes the insect to move. Most insects lose their exoskeleton in a phase called molting. During this phase, insects are very vulnerable to predators because the new exoskeletons have not hardened enough to protect them.
An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animal's body.
All arthropods (such as insects, spiders and crustaceans) and many other invertebrate animals (such as shelled mollusks) have exoskeletons.
Lobsters, for example, have tough outer shell systems which provide rigidity and shape to their bodies.