Chitin, a type of polysaccharide, is used to make the teeth of the radula (or biopolymer). Chitin can also be found in mollusk shells, crustacean and insect exoskeletons, and cephalopod beaks. The radula teeth, in particular, can vary significantly in size, shape, and several cusps on each of the different kinds (shown for Tryonia sp.), which include centrals, laterals, inner marginals, and outer marginals. These are important characteristics to consider when distinguishing between species. Furthermore, these characteristics reflect a gastropod's diet, though some gastropods have evolved to lose their radula entirely.