They spend their lives attached to rocks, plants, and other objects beneath the water's surface. Sponges cannot move about and were once thought of as plants, but since they do not manufacture their own food but must eat, they are classified as animals. There are over 5,000 species of sponges inhabiting oceans and fresh water bodies from warm shallow to cold deep waters. Coral is the limestone formation we often see as reefs, like the Great Barrier Reef of Australia, and is formed by millions of tiny animals. Coral formations may also take on the appearance of branching trees, domes or organ pipes.
Coral belongs in the same animal group as hydras, jellyfish, and sea anemones.
A coral polyp has a cylindrical body with a mouth, and anus at the open end, here are tiny tentacles used to capture prey. The other end of the coral attaches to the limestone skeletons of dead polyps. Most corals live in colonies, forming every shape and size imaginable, from a bowling ball to massive reefs surrounding entire islands. The stony or true corals attach themselves to each other with a flat sheet of tissue that connects to the middle of each body. As new polyps grow and develop, the limestone formation becomes larger.