Also called tetracoralla, the Rugosa are an extinct order corals that were abundant in Middle Ordovician to Late Permian seas.

Solitary rugosans are often referred to as "horn corals" because of a unique horn-shaped chamber with a wrinkled, or rugose, wall. Some solitary rugosans reached nearly a meter in length. However, some species of rugose corals could form large colonies. When radiating septa were present, they were usually in multiples of four.

Rugose corals were found from the Ordovician to the Permian and have a skeleton made of calcite that is often fossilized. Like modern corals, rugose corals were invariably benthic, living on the sea floor or in a reef-framework. Although there is no direct proof it is inferred that these Palaeozoic corals were provided with stinging cells to capture prey. Technically they are carnivores but prey-size was so small they are often referred to as microcarnivores.