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The phylum Porifera, which means "pore bearing," consists of three classes of sponges, which together contain more than 5,000 species. While these sponges share many common characteristics, each class has distinctive traits that set it apart from the others.
Of the 5,000 sponge species in the world, most dwell in marine waters, with only 150 of them living in fresh water. Each sponge is made up of a skeleton, composed of the fiber spongin, a mineral known as silica, or calcium carbonate. The skeleton supports a system of canals and pores through which water flows, driven by waving flagellae. The sponges feed on tiny plankton and bacteria that float through the sponge on the ocean's current. Each sponge can reproduce either sexually or asexually, and most are sessile, which means they are firmly attached to the ocean floor, rock or reef where they live and do not move, though a few are able to slowly crawl.
Ninety percent of the world's sponges are found within the class Demosponge, which alone contains 4,750 species. These sponges are asymmetrical, and sizes can vary from 3 millimeters to over 2 meters in length. They come in a variety of bright hues, ranging from yellow, orange and red to purple and green. Demospongiae can be found in all parts of the ocean, from the seashore to the farthest depths of the sea.
Hexactinellid sponges, also known as glass sponges, can be found all over the world, but are particularly populous in Antarctic Waters. These sponges stand upright to heights of up to 30 centimeters, forming strong bases that hold them to the ocean floor, with open central cavities that allow water to pass through. They may form symbiotic relationship with shrimp, who live inside the sponge's central cavity. A glass sponge with two shrimp inside is sometimes given as a wedding gift in Japan.
Calcarea are the only sponges whose skeletons are made of calcium carbonate. The class contains more than 400 species that can be found all over the world, but are most commonly found in temperate waters such as the Indian Ocean, at shallow depths less than 1,000 meters. These tiny sponges grow to less than 10 centimeters tall.
- University of California Museum of Paleontology: Introduction to Porifera
- Animal Diversity Web; Demospongiae: Kristen Wheeler
- University of California Museum of Paleontology: Demospongia
- Animal Diversity Web; Hexactinellida: Dan Atwater, Daphne G. Fautin
- University of California Museum of Paleontology: Calcarea
- Animal Diversity Web: Calcarea
- University of Arizona: Marine Discovery
- Polka Dot Images/Polka Dot/Getty Images