formally described species
||Sponges phylum Porifera
||Hentschel, U., Usher, K. M., and Taylor, M. W. (2006). Marine sponges as microbial fermenters. FEMS Microbiol. Ecol. 55, 167–177. doi: 10.1111/j.1574-6941.2005.00046.x p.167 left columnPubMed ID16420625
||Hooper NJA & van Soest RWM (2002) Systema Porifera: A Guide to the Classification of Sponges. Kluwer Academic/Plenum Publishers, New York.
||P.167 left column: "Sponges (phylum Porifera) are among the oldest metazoan animals, with a fossil record dating back more than 580 million years to the Precambrian. Sponges contribute significantly to, and sometimes even dominate, the tropical reef fauna in terms of biomass, but are also found in polar and deep oceans and in freshwater lakes and streams. Eighty-five percent of the 6000 formally described living species belong to the class Demospongiae (demosponges), with the other species being represented by the classes Hexactinellida (glass sponges) and Calcarea (calcareous sponges) (primary source)."