Demospongea
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Demospongea is a class of sponges differentiated by its silica or spongin spicules. The spicules either have one ray (monaxon) or four ray (tetraxon). This and other sponges are believed to have evolved near the start of the Cambrian period and still exist today. A lack of preservation due to the construction of their skeletons makes dating the first appearance of this class difficult.
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