(C8H13O5N)n is a long-chain polymeric polysaccharide of beta-glucose that forms a hard, semitransparent material found throughout the natural world. It is the main component of the cell walls of fungi, the exoskeletons of arthropods, such as crustaceans (e.g. crab, lobster and shrimp) and insects (e.g. ants, beetles and butterflies), the radula of molluscs and the beaks of cephalopods (e.g. squid, and octopuses). Chitin has also proven useful for several medical and industrial purposes.