A skeleton, or support structure, which supports the organism's body from the outside and is formed from the ectoderm. All arthropods (spiders, insects, crustaceans, horseshoe crabs, etc.) possess one. Compare endoskeleton. Any structure that is formed from the ectoderm in vertebrates, like nails, claws, hair, fur, horns, or teeth. (Note: does not include skin, which is an organ.)