Rugose corals are often called horn corals because many species have a horn shape. All horn corals live in a cup called a calyx (KAY-licks). The calyx often has radially alligned ridges or grooves, which are called septa. These septa were the skeletal support plates for the coral animal or polyp. When alive, the horn-shaped skeleton of the coral animal was attached to the sea floor with the pointy end down. The living coral polyp lived on the top of the skeleton with its arms or tentacles pointing upward.