exoskeleton

An exoskeleton is an external anatomical feature that supports and protects an animal's body, in contrast to the internal endoskeleton of, for example, a human. Whilst many many other invertebrate animals (such as shelled mollusks) have exoskeletons in the sense of external hard parts, the character is most associated with the arthropods (i.e. insects, spiders, myriapods and crustaceans). Exoskeletons contain rigid and resistant components that fulfil a set of functional roles including protection, excretion, sensing, support, feeding and (for terrestrial organisms) acting as a barrier against desiccation. Exoskeletons first appeared in the fossil record about 550 million years ago, and their evolution has been seen as critical as a driving role in the Cambrian explosion of animals that took place subsequent to this time.
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(n.)
The hardened parts of the external integument of an animal, including hair, feathers, nails, horns, scales, etc.,as well as the armor of armadillos and many reptiles, and the shells or hardened integument of numerous invertebrates; external skeleton; dermoskeleton.
  

Noun
1. the exterior protective or supporting structure or shell of many animals (especially invertebrates) including bony or horny parts such as nails or scales or hoofs
(hypernym) skeletal system, skeleton, frame, systema skeletale
(hyponym) carapace, shell, cuticle
(classification) invertebrate