The Sponges are the simplest of the multicellular animals. They usually attach to hard substrate where water movement is strong. The body wall has many small pores, called ostea.
Sponges are filter feeders.
Inflowing water flows in through a series of filter chambers which supply the sponge with unicellular algae and bacteria as food, provides oxygen and removes carbon dioxide in gas exchange, as well as removing excretory products and reproductive gametes. Click here to see how a sponge gets its food . A Photographic Guide to Seashore Life of Australia. New Holland, Sydney. Reed Books, Kew.