Chitin is a semitransparent material that is the main component of the exoskeletons of arthropods, such as crustaceans (e.g. crab, lobster and shrimp) and insects (e.g. ants, beetles and butterflies), of the cell walls of fungi, 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.