There are more than 5,000 species of sponges and they come in all shapes and sizes. Most are asymmetrical (not regularly shaped), though a few form "radially symmetrical" shapes (which means they can be divided into similar halves if cut at any angle along a central axis, like a pie). They are very simple animals with no tissues, organs, or even a brain, but have special cells that carry out their needs for food, circulation and reproduction.
