A large Cliona celata sponge growing on a silty limestone reef, Lyme Bay. Cliona celata occurs in two forms. It excavates channels in limestone (probably by chemical action) and may appear as small rounded pappillae protruding through the rock surface. It may also occur in raphyrus form, a large prominent colony, as in this image. The large form of Cliona celata is one of the most distinctive sponges found in UK waters. It is found in a wide range of conditions, exposed open coast to sheltered, silty areas. It is sometimes known as the sulphur boring sponge or yellow boring sponge.