Habitat: Reefs on rubble, commonly overgrowing other species. Characteristics: Thin (1-2 mm thick) crusts on the rubble (up to 100 cm2). Dark brown-red to purple externally, tan internally. Smooth surface. Oscules (1-2 mm wide), with transparent membranes and short radiating canals. Soft, easy to peel from substrate. Characteristics: Thin crust (1-4 mm), smooth to verrucose surface. Dark purple surface, tan interior. Aggressive reef species.