The chitinous exoskeleton of arthropods is formed by the polymerisation of: Lipoglycans, Keratin sulphate and chondroitin sulphate, D-glucosamine, N-acetyl glucosamine

N-acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid. Arthropods are covered with a tough, resilient integument or exoskeleton of chitin. Generally, the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. This happens in parts of the body where there is a need for rigidity or elasticity. Typically the mineral crystals, mainly calcium carbonate, are deposited among the chitin and protein molecules in a process called biomineralization. Chitin is the polymer of N-acetyl glucosamine units.