Chitin

chitin \ˈkī-t^ən\ noun: a horny polysaccharide (C8H13NO5)_n that forms part of the hard outer integument especially of insects, arachnids and crustaceans (chitinous \ˈkī-t^ən-əs, ˈkīt-nəs\ adjective)

Etymology: French chitine, from Greek chitōn

I am not going to make a joke about horny polysaccharides.