Which type of coral is not classified as hard coral?

Sea fans are classified as soft corals, which distinguishes them from hard corals. Hard corals, such as staghorn, brain, and elkhorn corals, possess a calcareous skeleton that provides structural support and contributes to reef building. In contrast, sea fans lack this rigid skeleton; instead, they have a flexible, branching structure made primarily of a protein called gorgonin. This characteristic allows soft corals like sea fans to thrive in varying environments, often in deeper waters or areas with strong currents where hard corals might be less successful. The flexibility of their structure helps them withstand the forces of water movement, unlike the stiffer skeletons of hard corals, which are more vulnerable to physical damage in such conditions.