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.

[2] The yellow boring sponge is native to the north-eastern Pacific Ocean, its range extending from Alaska to Baja California.

[2] A newly settled young sponge makes its way to the shell of a suitable host and bores into a valve of the mollusc (or the plates of the barnacle).

[2] Its tunnelling activities weaken the shell, and scallop and oyster farmers consider the sponge to be a pest.

[3] These sponges are common growing on the thick-shelled giant rock scallop (Crassadoma gigantea) and on oysters.