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Sponges are considered the oldest of the animal phyla. The name Porifera means "pore bearer" in Latin. The surface of a sponge's body is covered by a skin, one cell thick. This skin is penetrated by numerous small pores and a few large openings. These are respectively the entrances and exits for a complex system of canals and chambers through which the sponge pumps a current of water. The body of the sponge between this system of canals is a loose assemblage of about six different types of specialized cells that secrete a supporting skeleton of collagen fibers and mineral spicules (glass or calcium carbonate) and carry out the processes of growth, repair, nourishment, and reproduction.
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