Plexauridae Family of Gorgonians
Two Gorgonians of the Plexauridae Family can be found in this website:
California Golden GorgonianPhylogeny: Plexaurid Gorgonians are octocoral members of the Plexauridae Family. Like hydroids, jellyfish and sea anemones they belong to the phylum Cnidaria. They are the subphylum Anthozoa, the class Octocorallia, and the order Malacalcyonacea. The Plexauridae Family is one of forty-nine families in this order. The Plexauridae Family contains five genera and ninety-one species. The name Plexauridae comes from the name Plexaure, who was a nymph from Greek mythology. In Mexico, the family is known as Arbolitos del Mar.
Morphology: As octocorals, Plexaurid Gorgonians lack the hard calcium carbonate skeletons of stony corals and are often called soft corals. The polyps have eight-fold radial symmetry, with eight pinnate (having a feather-like appearance) tentacles. The polyps have a hollow digestive cavity, and specialized stinging structures in the tentacles that surround the mouth. Their polyps have a flower-like appearance. Plexaurid Gorgonian polyps have tentacles that are retractable. 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. The central core of the branches is hollow and composed of a horn-like substance called gorgonin. Gorgonin is comprised of bromine and iodine, with a protein that is exclusive to gorgonians. 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 or raised, with just the tentacles and mouth exposed. The colonies may be bushy, rod-shaped, or fan-shaped. Species in this family may form colonies up to 90 cm (35 inches) in breadth. Plexaurid Gorgonians differ from Gorgonians in the Gorgoniidae Family in that those Gorgonians have solid cores which contain sclerites and sclerites that are less than 0.3 mm in length.
Habitat and Distribution: Plexaurid Gorgonians are found attached to hard surfaces including corals, mudstones, pilings, rocks and wreckage. Most Gorgonians are found in shallow waters where there is more sunlight and ample water movement, but some are found at depths exceeding 2,200 m (7,200 feet). Plexaurid Gorgonians are found worldwide in polar to tropical seas. At least twelve species from this family are found in Mexican waters.
Reproduction: Plexaurid Gorgonians colonies are gonochoric (male or female). Sexual reproduction is accomplished through broadcast spawning, with external fertilization. The gametes are shed into the coelenteron and spawned through the mouth. The zygote develops into a planktonic planula larva. Metamorphosis begins with early morphogenesis of tentacles, septa and pharynx before larval settlement on the aboral end. Reproduction may also be asexual, through fragmentation or budding.
Ecosystem Roles: Plexaurid Gorgonians are sessile suspension feeders that use their polyp tentacles to capture drifting food from the water column. They feed on plankton and suspended organic matter. Some Plexaurid Gorgonians are zooxanthellate, meaning that have a symbiotic relationship with single-cell dinoflagellates called zooxanthellae. Zooxanthellae live within certain coral polyps, jellyfish, nudibranchs and sea anemones. The zooxanthellae produce energy, during daylight, by means of photosynthesis with the energy being passed along to their hosts, sometimes providing up to 90% of the host’s total energy requirements. In return, the host provides carbon dioxide, nutrients, and a secure, sunlit, dwelling for the zooxanthellae. Plexaurid Gorgonians are preyed upon by fish, gastropods, nudibranchs, and sea stars. Some of the nudibranchs that feed on these corals are remarkably camouflaged to blend in with their hosts.