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Octocorals ...

• are the sea fans, sea plumes, soft corals, sea pens, sea rods, gorgonians and their relatives;
• belong to the major group, or phylum, of the Animal Kingdom that also includes the stony corals, sea anemones, black corals, jellyfishes, hydroids, and Portuguese man o' war;
• like other members of the phylum, have cells that produce microscopic stinging capsules called cnidae (“NYE-dee”) for feeding and defense, although none cause a painful reaction in humans;
• grow as colonies of small, interconnected, bag- or cup-like polyps, each composed of two tissue layers, with a mouth surrounded by a ring of tentacles, but no anus;
• have polyp anatomy arranged radially around the mouth like wheel spokes: eight pinnate tentacles and an interior digestive/circulatory chamber divided by eight partitions (thus, “octo” corals);
• like stony corals and anemones, lack the swimming medusa (“jellyfish”) stage found in many hydroids and fire coral;
• include many reef-dwellers that harbor symbiotic, single-celled dinoflagellate algae called zooxanthellae, that contribute to the colony’s nutrition;
• also include many deep-water species that feed chiefly on plankton;
• chiefly grow as either male or female colonies, although just under 10% of species are hermaphroditic;
• can in some cases reproduce asexually through fragments that can give rise to another colony;
• grow into a distinctive shape or vary depending upon factors such as currents and light;
• live exclusively in the ocean, cemented to the seafloor (although a few deep-sea species, and the sea pens, anchor in sand or mud, and their larvae can crawl or swim);
• range from small mats that encrust rocky seafloors to tree-like colonies 3 meters tall (a few species are small solitary polyps);
• number over 3,100 species;
• often require microscopic examination of skeletal structures for identification.

• are widespread, common and often dominant components of shallow-water marine communities on hard substrates, including reefs and rocky bottoms;
• number over sixty species;
• often outnumber stony coral species and may represent a greater percent of living biomass in local reef and rocky bottom habitats;
• are well known but in some cases are difficult to distinguish.