Habitat: Generally inhabit deep reefs and walls, occasionally shallower. Prefer shaded areas on rocky substrates and also grow in low-light conditions under ledge overhangs and in cave openings. Polyp tentacles retracted during the day. Characteristics: Single, large, fleshy, circular to oval polyp. Underlying skeleton often evident in the form of raised radiating lines. Central area of corallite usually flat to somewhat convex, rarely concave. Darked shades of gray to brown, green, and brlue-green; base color often radially streaked with lighter shade. May fluoresce.