octocorals

Octocorals are a clade of marine cnidarians within the subclass Octocorallia of the class Anthozoa. They include soft corals, sea fans, sea whips, and sea plumes. A defining feature is their eightfold symmetry: polyps have eight tentacles and eight mesenteries arranged in eightfold patterns.

Most octocorals lack a rigid external skeleton. Instead, they possess a flexible internal skeleton composed of a protein matrix called gorgonin, often reinforced by calcareous sclerites embedded in the tissue. A minority, notably the blue corals in the order Helioporacea, have a solid calcite skeleton.

Colonies are typically colonial, with many genetically identical polyps linked by tissue. Growth forms range from branching and fan-like structures to encrusting sheets and whip-like thickets. Distribution is worldwide in both tropical and temperate seas, from shallow reefs to deep-sea habitats. Feeding is mainly by catching small plankton with their tentacles, though some shallow-water species host symbiotic algae (zooxanthellae) and gain energy from photosynthesis.

Reproduction occurs sexually and asexually: polyps can bud to propagate colonies, and most species release eggs and sperm or brood young, sometimes synchronously. Ecology and conservation: Octocorals contribute complex habitat structure and shelter for many marine organisms. They are threatened by climate change, ocean acidification, and physical disturbance, as well as collection pressure for the live trade and jewelry in some regions. Some regions regulate octocoral harvesting through wildlife or fisheries laws.

Notable groups include the soft corals and gorgonians of Alcyonacea, and the blue corals of Helioporacea.