Characters: Colonies are unifacial laminae, usually horizontal, but may develop upright ridges or columns. They commonly form stands several metres across. More than one row of corallites may occur between ridges. Columellae are absent. Colour: Pale brown to deep grey, often with pale margins. Similar species: Pachyseris gemmae. Habitat: All reef habitats but most common on lower reef slopes. Abundance: Common.