Octocorallia

Octocorallia, or octocorals, is a subclass of Anthozoa within the phylum Cnidaria. Members are mostly sessile marine animals that form colonies or occur as solitary polyps. They are characterized by eightfold (octamerous) symmetry, most notably polyps with eight tentacles and eight mesenteries in the gastrovascular system. The supporting skeleton is typically internal and flexible, often composed of a proteinaceous matrix with embedded calcareous sclerites; some groups have different skeletal compositions, such as the rigid skeletons seen in blue corals and the chitinous skeleton of black corals.

The subclass includes several orders, most prominently Alcyonacea (soft corals and gorgonians like sea fans and sea whips), Pennatulacea (sea pens), Antipatharia (black corals), and Helioporacea (blue corals). Together these organisms occupy a wide range of habitats from shallow tropical reefs to deep-sea environments. Many octocorals are colonial, forming delicate, branching structures that provide habitat and shelter for a variety of marine life. Sea pens (Pennatulacea) are anchored in soft sediments and extend feather-like pinnate polyps above the substrate.

Reproduction in Octocorallia is diverse, with sexual reproduction through broadcast spawning or brooding as well as asexual modes such as fragmentation and budding, enabling colony expansion. Many species release planula larvae that disperse before settling to form new colonies. Distribution is global, but diversity and growth strategies vary with depth, temperature, and substrate.

Conservation concerns include overharvesting, especially of black and blue corals for jewelry and ornamentation, and threats from habitat destruction, pollution, and climate change. Because many octocorals grow slowly, their recovery from disturbance can be prolonged.