This species is usually covered with Polyzoa, Lithothamnion, and other adherent matter, which obscures its appearance, but the shell itself is so rude, spongy, and bleached in appearance that the actual surface is often discriminated only when examined with a lens.
It favours rock pools and smooth rock covered with encrusting red algae such as Lithothamnion on which it feeds.
It is usually found on stones and boulders, especially those encrusted with red crustose algae such as Lithothamnion.
Lithothamnion | A small specimen of ''Mopalia mucosa'' covered in and surrounded by encrusting ''Lithothamnion |