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An exoskeleton is a hard external skeleton that protects the outer surface of an organism and enables movement through muscles attached on the inside. An endoskeleton is an internal skeleton composed of hard, mineralized tissue that also enables movement by attachment to muscles. The endoskeleton is mainly found inside of vertebrates, which are mammals, birds, fishes, amphibians, and reptiles, whereas the exoskeleton is found outside of invertebrates like insects, spiders, crabs, centipedes, and millipedes. There are few vertebrates with both exoskeleton and endoskeleton protecting their body.