Cliona californiana, the yellow boring sponge, boring sponge or sulphur sponge, is a species of demosponge belonging to the family Clionaidae. It is native to the north-eastern Pacific Ocean and burrows into the shell valves of bivalve molluscs.

Description The yellow boring sponge inhabits living bivalve molluscs, boring into the shell valves. The only parts of the sponge which are visible from the outside are small yellow patches up to 3 mm (0.1 in) in diameter, sometimes containing small oscula (openings). The sponge spicules are silicaceous (glassy) and are scattered throughout the sponge tissues. They consist entirely of megascleres known as "tylostyles", which are a kind of spicule with a single shaft, with a point on one end and a knob on the other. These characteristic spicules distinguish this sponge from any other sponge species found in the locality.

Distribution and habitat The yellow boring sponge is native to the north-eastern Pacific Ocean, its range extending from Alaska to Baja California. It is most often found in the subtidal zone but also occurs in the intertidal zone. It is more common in the colder waters in the northern part of its range than it is in the southern part, and it occurs at depths down to about 120 m (400 ft).