A large rounded sponge up to 15 cm in diameter and height up to 10 cm. The consistency is firm-hard, but slightly compressible. The smooth surface is bluish or violet-grey and extensively perforated with inhalant orifices. Larger exhalant openings (osculum) are distinct and usually in lines or arranged in clusters. The skin (cortex) is distinct and 1 mm thick, underneath the surface the colour is yellow-white.