Unlike plant cell walls, a fungus’s cell wall is composed of chitin—called a polysaccha-ride or nitrogenous substance—and one that is most often found in the outer skeleton (exoskeleton) of certain land animals, such as grasshoppers, and outer shells of some marine animals, such as crabs and mollusks. (To compare, the cell walls of plants and some protists are composed of cellulose.) The rigidity of the chitin is for protection and also helps to slow down dehydration of the fungi, especially in times of drought.