Many-celled animals: Metazoa
• PHYLUM 1. SPONGES, OR PORIFERA.
A sponge is about as simple as a many-celled animals can be. Sponges are colonial-that is, many of the little animals clump together. They never move about. They live in water. They have either radial symmetry or none at all. The two-layered body encloses a cavity punctured by small pores that let water in. The animal takes food particles and oxygen from then the water, and than the water goes out through a single big opening. The bath sponge or the sponge that you wash cars with is just the skeleton of a sponge with all the live parts gone. There are about 3,000 species of sponges.