An exoskeleton (from Greek έξω éxō "outer"[1] and σκελετός skeletós "skeleton"[2][3]) is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. that of a human) which is enclosed underneath other soft tissues. Some large, hard and non-flexible protective exoskeletons are known as shell or armour.
Examples of exoskeletons in animals include the cuticle skeletons shared by arthropods (insects, chelicerates, myriapods and crustaceans) and tardigrades, as well as the skeletal cups formed by hardened secretion of stony corals, the test/tunic of sea squirts and sea urchins, and the prominent mollusc shell shared by snails, clams, tusk shells, chitons and nautilus. Some vertebrate animals, such as the turtle, have both an endoskeleton and a protective exoskeleton.
- ^ Liddell, Henry George; Scott, Robert (1940). "ἔξω". A Greek-English Lexicon. Perseus Digital Library.
- ^ Liddell, Henry George; Scott, Robert (1940). "σκελετός". A Greek-English Lexicon. Perseus Digital Library.
- ^ Douglas, Harper (2001). "exoskeleton". Online Etymology Dictionary. Archived from the original on 20 April 2013.