The Demospongiae class is the largest in the phylum Porifera. Their skeletons are made the protein sponging. The Protein sponging makes up 90% of all sponges. Most are found in the ocean, but several live in freshwater environments. Some are brightly colored, and there is great variety in body shape.

 

Photo Credit: This image is in the public domain because it contains materials that originally came from the U.S. National Oceanic and Atmospheric Administration, taken or made during the course of an employee's official duties.

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http://www.mbnms-simon.org/other/photos/photo_info.php?photoID= 2081&search=kw&keywordSearchTerm=sponge&s=0&page=1 |Date=2007-04-18 |Author=SIMoN / MBNMS |Permission=All SIMoN phot)