Chitin

Chitin is the second most abundant natural biopolymer in the world, behind only cellulose. It is also the most abundant naturally occurring polysaccharide that contains amino sugars. This abundance, combined with the specific chemistry of chitin and its derivative chitosan, make for the array of potential applications.
Chitin occurs as a component of crustacean shells, insect exoskeletons, fungal cell walls and plankton, it is found in association with proteins and minerals such as calcium carbonate. The different sources of chitin differ somewhat in their structure and percentage of chitin content.