This group includes insects, spiders, crustaceans, and other invertebrates with jointed legs, segmented bodies, and hard exoskeletons. Arthropods are the most diverse group of animals on Earth, with over a million species.
Some mollusks, such as snails and slugs, have a hard shell or plate-like structure on the outside of their bodies. This shell serves as protection from predators and the environment.
Echinoderms, such as starfish and sea urchins, have a hard, spiny exoskeleton made of calcium carbonate. This exoskeleton provides support and protection for the animal's internal organs.
Annelids, such as earthworms and leeches, have a segmented body with a tough, flexible outer layer that protects them from predators and the environment.
Crustaceans, such as crabs and lobsters, have a hard exoskeleton that covers their entire body. This exoskeleton provides support and protection, as well as a surface for muscle attachment.