The sponges have a simple body plan. Its body, the central cavity is surrounded by a wall that has thousands of openings, or pores. A current of water that enters these pores are powered by the flagella of cells called collar cells. The water exits through a large hole called osculum.The skeletal system of the sponges are composed of spicules. These spicules are made of calcium carbonate and are secreted by special cells called amoebocytes.
Other kinds of sponges have skeletal system made of spongin. Cells of the body grow around these fibers and are thus supported by the protein matrix.
For commercial harvest, the sponges are dried and washed to remove the cells and the protein meshwork. Then, they are sold as natural sponges for bathing or washing cars.
Deep ocean sponges, called glass sponges, have elaborate skeletons made from silica that support the cells of the body. The elaborate structure of glass sponges are shown below. For a detailed explanation, go to http://www.promotega.org/ksu00019/glass_sponges.htm
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