Most hard or stony corals live as colonies of polyps that secrete a rigid external skeleton of lime. But there are also those that live as solitary individuals.
Corals grow in a wide variety of forms as the types here demonstrate.
Sea fans, for example, have an internal skeleton linking the polyps, while the polyps of the brain coral are arranged in rows. The stagshorn coral gets its name from the resemblance of the colony to a male deer's antlers. The names of the plate and pillar corals also reflect their appearance.