The colonies are usually about 2.4 cm across. Some colonies form a carpet over a metre across. Sponges grow on rocks, but more commonly on submerged sticks and branches. They usually look like soft blobs of old foam cushion. In colour, they are a dull creamy brown to medium brown.
Many colonies take on a green colour because they contain algae.
The algae are trapped in the pockets or pores that go all through the sponge. To keep the sponges from collapsing, sponge animals produce rod-like 'spicules' or pillars of silica. Silica is the main substance that makes up sand or glass. The hard spicules, along with the unpleasant smell of wastes given off by the sponge, help protect the sponge from predators. Some small animals are able to attack the soft, jelly-like cells inside the sponge.