Birds are warm-blooded animals with feathers and wings. Most mammals also have body hair. Invertebrates Sponges are the most primitive of animal groups. Coelenterates are also very primitive. Their mouths, which take in food and get rid of waste, are surrounded by stinging tentacles.
Some coelenterates are jellyfish, corals, and sea anemones.
Echinoderms include starfish, sea urchins, and sea cucumbers. They live in seawater and have external skeletons. Mollusks are soft-bodied animals, which often live in hard shells. They include snails, slugs, octopus, squid, mussels, oysters, clams, scallops, chitons, and cuttlefish. Mollusks are the second-largest group of invertebrates, with 50,000 living species.