Characters: Colonies form flat, unifacial, explanate or encrusting plates, commonly arranged in whorls. Corallites are in concentric valleys. Centres are widely spaced (3-5 per cm). Long and short septo-costae clearly alternate. Colour: Rust brown, usually with pale margins. Mouths are white and star-shaped, a useful identification aid. Similar species: Agaricia grahamae, which is usually distinguished by lack of white mouths, and septo-costae which do not alternate and are thicker than the spaces between them. Habitat: Shallow reef environments. Abundance: Common.