The phylum of marine and freshwater invertebrates that comprise the sponges, which live permanently attached to rocks or other surfaces. The body of a sponge is hollow and consists basically of an aggregation of cells between which there is little nervous coordination. The body is supported by an internal skeleton of spicules of chalk, silica, or fibrous protein (bath sponges have protein skeletons). Undulipodium-bearing (flagellated) cells (choanocytes) cause water to flow in through openings ( ostia) in the body wall and out through openings ( oscula) at the top; food particles are filtered from the water by the choanocytes. See also Placozoa.
http://animaldiversity.ummz.umich.edu/site/accounts/information/Porifera.html Overview of the sponges, including their biology and classification, from the University of Michigan's Museum of Zoology Diversity Web
Subjects: Biological Sciences.