WREMA.86.247.50.9 - Rugose corals are now extinct. This one is over 300 million years old. Most corals today live in colonies, or reefs, made up of many small corallites. Some rugose corals were larger solitary forms. They often have this distinctive horn shape. The base was anchored into the sea floor, with the living polyp in the hollow at the top. It fed by filtering particles out of sea water with its tentacles.