• PHYLUM 2. COELENTERATA, OR COELENTERATES.
These are the corals, jellyfishes, sea anemones and some creatures called hydroids. The coelenterates have radial symmetry. The body cavity is simple sac of two layers. In some the body is slim and cylindrical. In others, like the jellyfish, it is swollen into a sphere by a mass of watery stuff between the two body layers. A set of stinging cells in the tentacles of some is used both for protection and in paralyzing the little animals that they eat. It is because of these stinging cells that people stay away from some bathing beaches in jellyfish season. Some of the corals live in large colonies. When they die, their hard skeletons build up islands or reefs. There are some 4,500 species of coelenterates known. All live in water.