The tentacles of Colonial Cup Coral (Tubastraea coccinea) rarely extend completely during the day, unless current or surge is bringing food to the coral. At night, when the water carries more plankton, the tentacles extend to trap their food. Colonial Cup Coral is often found on the roof of caves and overhangs; unlike many corals, it does not have photosynthetic zooxanthellae and does not need sunlight to make its food.

This coral was photographed  in about 35 feet of water on the underside of a lava formation off the south Kohala Coast near the Mauna Lani Resort on the Big Island of Hawaii.