All sponges live in water, from the deepest seas to the shallow coastal waters. They range in size from over 1 meter (3 feet) long to 2 millimeters (less than 1/8 of an inch) long. Sponges are sessile they are attached to one place and do not move around. Sponges also lack symmetry, true organs, a digestive or respiratory system, a nervous system, muscles, and a true mouth.

This lack of true tissue layers makes sponges different from all other animals except protozoans, which are not multicellular. Although sponges are made up of many cells with specialized functions, their cells are not organized into true tissues. Evidence for this comes from specialized cells called choanocytes which sponges use in feeding. Sponges arose 550 million years ago in the pre- Cambrian period, evolving from colonial protists, groups of identical single cell organisms that live together. This also makes Porifera the simplest in form and function. Phylogenetically, Porifera is most closely related to Protista, making it the first animal phylum to have evolved to be multicellular. The phylum Porifera contains all the species of sponges.

Water moves through sponges