Chitin is a major constituent of the exoskeleton, or external skeleton, of many arthropods such as insects, spiders, and crustaceans. Exoskeletons made of this durable and firm compound support and protect the delicate soft tissues of these animals, which lack an internal skeleton. Chitin is a polysaccharide, a type of carbohydrate that has a basic structure of a repeating chain of sugar molecules. Chitin is analogous in structure to cellulose, the compound that provides structural support to plant tissues. In addition to being found in arthropod exoskeletons, chitin is also found in the cell walls of some species of fungi.

The exoskeleton of the Cayman Islands stone crab is made up, in part, of the polysaccharide chitin.

Chitin does not work alone in forming exoskeletons. It is associated with a number of proteins, including an elastic, rubberlike substance called resilin. The identity and nature of these proteins determines...