Colpophyllia natans, known as boulder brain coral and large-grooved brain coral, is a species of stony coral found primarily in the Caribbean Sea and the Gulf of Mexico. It inhabits the slopes and tops of reefs, to a maximum depth of fifty metres. It is characterised by large, domed colonies, which may be up to two metres across, and by the meandering network of ridges and valleys on its surface. The ridges are usually brown with a single groove, and the valleys may be tan, green, or white and are uniform in width, typically 2 centimetres. The polyps only extend their tentacles at night.