Characters: Colonies are dome-shaped with an even surface and may be up to 2 metres high and 5 metres across. The skeleton is dense. Corallites form low cones with small openings and very thick walls. Columellae are large. Septa are equal and are thick at the wall and thin where joining the columellae. Tentacles are extended only at night. Colour: Usually uniform cream or grey, sometimes greenish. Similar species: None. This is one of the most easily recognised and least variable of all massive corals. Habitat: Both exposed and protected reef environments. Abundance: Sometimes common.