Open brain coral

Open brain corals can be solitary or colonial.[2] They are small corals, rarely reaching over 20 cm in diameter.[3] They are free-living and exhibit a flabello-meandroid growth form, meaning they have distinct valley regions separated by walls.[4][5] In colonial forms, the valley regions can contain multiple individual polyps.[5] Complexity of valley regions can range; some are hourglass shaped while other cans be highly lobed.[2] They typically have bilateral symmetry.[4] During the day when the polyp is closed, the coral is covered by a mantle that extends beyond the skeleton, but can retract when disturbed.[4][5] Polyps and mantle are very fleshy.[4] Colonies can be blue, green, yellow, brown, and are often vibrantly colored.[4][5]

The open brain coral is known to host a species of gall crab, Lithoscaptus semperi.[6]

A red variety of Trachyphyllia in a reef aquarium

Open brain corals can be found throughout the Indo-Pacific, from the Red Sea to New Caledonia. They are found up to a maximum depth of 40 meters.[3]

Open brain corals are less common directly in coral reef communities, and are more often found on sandy reef slopes, around continental islands, and lagoons.[2][5][3] Open brain corals can often be found near other free-living corals.[3][7] Large colonies of open brain corals are uncommon, and are typically only observed in marine protected areas.[3]

The IUCN lists open brain corals as "near threatened" due to habitat loss and over-harvesting for the aquarium trade.[3] The biggest exporter of open brain coral is Indonesia. In 2005, Indonesia exported over 60,000 open brain corals for use in the aquarium trade.[3]

Other threats to open brain corals include disease, acidification, and severe storms.[3]