Gorgonians are an octocoral that are members of the Plexauridae Family. Like hydroids, jelly fish and sea anemones they belong to the Phylum Cnidaria as they have radial symmetry, a hollow digestive cavity, and specialized stinging structures in the tentacles that surround the mouth. In Mexico, the family is known as arbolitos del mar. They are in the Class Anthozoa, with their polyps have a flower-like appearance. They are in the sub-class Octocorallia or Octocoral that are also known as Alcyonaria. The Octocorals are colonial organisms that have eight-fold radial symmetry with eight pinnate (having a feather-like appearance) tentacles. They lack the hard calcium carbonate skeletons of Stony Corals and are often called Sofeet Corals. In place of a hard skeleton, they have tiny spine-like parts in their bodies called sclerites (or spicules) that gives them some level of support. Colonies may be branch-like, bushy, encrusting or fan-like. The Octocorals include the feather plumes, sea fans, sea rods and sea whips.
The Plexauridae Family includes soft corals whose sclerites are less than 0.3 mm in length. The colonies may be bush or fan shaped with the branches having a hollow axial core that does not contain sclerites and is composed of a horn-like material call gorgonin. Gorgonin is a protein which is exclusive to the gorgonians and which contains significant amounts of iodine and bromine. In Plexauridae Gorgonians, the sclerites are embedded in the polyp tentacles and in the coenenchyme which surrounds the core. These sclerites range from 0.3 mm to 5.0 mm in length. Because of these large sclerites, many species in the Family have a tuberculate or thorny texture. The material surrounding the openings in the coenenchymes (from which the polyps emerge) is called calyx or calyces. They may be flush with the surface of the ocean bed or raised, with just the tentacles and mouth exposed. Gorgonian in the Plexauridae Family have tentacles that are retractable. They differ from those in the Gorgonidae Family in that those Gorgonians have solid cores which contain sclerites and sclerites that are less than 0.3 mm in length.
Gorgonians begin life as planktonic larvae. When they settle on to a suitable hard surface, they attach and become sessile. Because they cannot chase their food, they depend on water currents to supply them with sufficient planktonic food such as fish larvae and amphipods. Sofeet Corals are prey for fish, starfish, and gastropods. Some of the nudibranchs that feed on these corals are remarkably camouflaged to blend in with their hosts. Like Hard Corals, some Gorgonians are zooxanthellate. This means that they have a symbiotic relationship with single-cell dinoflagellates, known as zooxanthellae. Zooxanthellae live within certain coral polyps, Sea Anemones, Jellyfish, and Nudibranchs. The zooxanthellae produce energy, during daylight, by means of photosynthesis. This energy is passed along to their hosts, sometimes providing up to 90% of the host’s total energy needs. In return, the host provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zooxanthellae.
Gorgonians are the most prominent tropical corals found along both coasts of the Americas. They are also more prolific in the Americas than in any other location. These Gorgonians are found in the Pacific and Atlantic Oceans, in tropical, temperate and polar waters. Most Plexauridae Gorgonians are found in shallow waters where there is more sunlight and water movement, but some are found at depths that exceed 2,200 m (7,200 feet). They are found attached to hard surfaces including rock, coral, pilings, and wreckage. There are 370 species in the Plexauridae Family of which 9 are found along the Pacific Coast of Mexico.