It is a primary component of cell walls in fungi (especially filamentous and mushroom-forming fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms.

Chitin is a large, structural polysaccharide made from chains of modified glucose. Chitin is found in the exoskeletons of insects, the cell walls of fungi, and certain hard structures in invertebrates and fish.

Activation of cell wall compensatory or salvage mechanisms often results in elevated chitin levels in the cell wall and an increase in the number of GPI proteins that are covalently attached to chitin rather than β-(1,3) glucan, reflecting significant alterations to cell wall architecture .

Most fungi have a common inner wall skeleton of chitin and β-glucans that functions as a flexible viscoelastic frame to which a more diverse set of outer cell wall polymers and glycosylated...