scler·o·tin 
(sklîrə-tĭn, sklĕr-)
(sklîrə-tĭn, sklĕr-)n.
An insoluble protein in the cuticle of arthropods that is hardened and darkened by cross-links with quinones and is often bound to chitin filaments.
[SCLERO- + -tin (as in KERATIN or CHITIN).]