The hard rigid covering of animals including MOLLUSCS; TURTLES; INSECTS; and crustaceans.

Shells of marine animals most often composed of CALCIUM CARBONATE.

Synonyms: Shell, Animal, Animal Exoskeletons, Shells, Animal, Animal Exoskeleton, Seashell, Exoskeletons, Animal, Seashells, Carapaces, Exoskeleton, Animal, Animal Shells, Animal Shell, Carapace