This section showcases crabs, lobsters, shrimps, hermit crabs, and barnacles that are members of another large group called 'Arthropoda'. Including the terrestrial members, this is the largest group of animals on the planet. They have a hard outer covering or exoskeleton made of a material called 'chitin', and have legs with joints. Land-dwelling arthropods are usually smaller than the marine arthropods that can grow really big. Most marine arthropods are crustaceans - a group that includes crabs, lobsters, barnacles, etc.