Chitin

Chitin (C8H13O5N)n (/ˈkaɪtɨn/ KY-tin) is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. It is the main component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulae of molluscs, and the beaks and internal shells of cephalopods, including squid and octopuses. The structure of chitin is comparable to the polysaccharide cellulose, forming crystalline nanofibrils or whiskers. In terms of function, it may be compared to the protein keratin. Chitin has also proven useful for several medical and industrial purposes. In butterfly wing scales, chitin is often organized into stacks of nano-layers or nano-sticks made of chitin nanocrystals that produce various iridescent colors by thin-film interference: similar, analogous structures made of keratin are found in iridescent bird plumage.
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