Lobsters
The lobster has a skeleton type that provides defense against predators, supports the body, and allows for movement through the contraction of attached muscles. As with vertebrates, muscles must cross a joint inside the exoskeleton. Shortening of the muscle changes the relationship of the two segments of the exoskeleton. Arthropods, such as crabs and lobsters, have exoskeletons that consist of 30–50 percent chitin, a polysaccharide derivative of glucose that is a strong-but-flexible material. The exoskeleton is further strengthened by the addition of calcium carbonate in organisms like the lobster. Because the exoskeleton is acellular and does not grow as the organism grows, lobsters or other animals like it must periodically shed their exoskeletons.