The substance that makes up the hard outer skeletons of certain animals is called?

The substance that makes up the hard outer skeletons of certain animals is called chitin. It is a tough, flexible material that is composed of long chains of sugar molecules. Chitin is found in the exoskeletons of insects, crustaceans, and some other invertebrates. It is also found in the cell walls of some fungi. Chitin is a strong and lightweight material, making it ideal for use in protective structures. It is also biodegradable, making it an environmentally friendly material.