Sponges come in two basic types: encrusting or free-standing. Although neither of these names are part of the true classification of sponges, it does make it a bit easier to organize them.

Encrusting sponges typically cover the surface of a rock in the same manner that moss covers a rock on land.

Yellow sponge

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Encrusting sponge

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Bath sponge
(The "skeleton" of the bath sponge)

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