Alcyonacea is the old scientific order name for the informal group known as "soft corals". It is now an unaccepted name for class Octocorallia. It became deprecated . The following text should be considered a historical, outdated way of treating the

taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...

Anthozoa Anthozoa is one of the three subphyla of Cnidaria, along with Medusozoa and Endocnidozoa. It includes Sessility (motility), sessile marine invertebrates and invertebrates of brackish water, such as sea anemones, Scleractinia, stony corals, soft c ...

and Octocorallia. Some, or many parts of it, are no longer valid. Any remaining information found to be still valid, should be carefully merged into Octocorallia. Alcyonacea are an order of sessile colonial

cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

ns that are found throughout the oceans of the world, especially in the deep sea, polar waters,

tropics The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and subtropics. Whilst not in a strict taxonomic sense, Alcyonacea are commonly known as soft corals. The term "soft coral" generally applies to organisms in the two orders Pennatulacea and Alcyonacea with their polyps embedded within a fleshy mass of coenenchymal tissue. Consequently, the term "gorgonian coral" is commonly handed to multiple species in the order Alcyonacea that produce a mineralized skeletal axis (or axial-like layer) composed of calcite and the proteinaceous material gorgonin only and corresponds to only one of several families within the formally accepted taxon Gorgoniidae ( Scleractinia). These can be found in order Malacalcyonacea (taxonomic synonyms of include (unaccepted): Alcyoniina, Holaxonia, Protoalcyonaria, Scleraxonia, and Stolonifera. Common names for subsets of this order are sea fans and sea whips; others are similar to the sea pens of related order Pennatulacea. Individual tiny polyps form colonies that are normally erect, flattened, branching, and reminiscent of a fan. Others may be whiplike, bushy, or even encrusting. A colony can be several feet high and across, but only a few inches thick. They may be brightly coloured, often purple, red, or yellow. Photosynthetic gorgonians can be successfully kept in captive aquaria. About 500 different species of gorgonians are found in the oceans of the world, but they are particularly abundant in the shallow waters of the Western Atlantic, including

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

Bermuda Bermuda is a British Overseas Territories, British Overseas Territory in the Atlantic Ocean, North Atlantic Ocean. The closest land outside the territory is in the American state of North Carolina, about to the west-northwest. Bermuda is an ...

, and the West Indies.

Anatomy

The structure of a gorgonian colony varies. In the suborder Holaxonia, skeletons are formed from a flexible, horny substance called gorgonin. The suborder Scleraxonia species are supported by a skeleton of tightly grouped calcareous spicules. Also, some species encrust like coral. Measurements of the gorgonin and calcite within several long-lived species of gorgonians can be useful in paleoclimatology and paleoceanography, as their skeletal growth rate and composition are highly correlated with seasonal and climatic variation.

Features

Soft corals contain minute, spiny skeletal elements called sclerites, useful in species identification. Sclerites give these corals some degree of support and give their flesh a spiky, grainy texture that deters predators. In the past, soft corals were thought to be unable to lay new foundations for future corals, but recent findings suggest that colonies of the leather-coral genus '' Sinularia'' are able to cement sclerites and consolidate them at their base into alcyonarian spiculite, thus making them reef builders. Unlike stony corals, most soft corals thrive in nutrient-rich waters with less intense light. Almost all use symbiotic photosynthetic zooxanthella as a major energy source. However, most readily eat any free-floating food, such as zooplankton, out of the water column. They are integral members of the reef ecosystem and provide habitat for fish, snails, algae, and a diversity of other marine species. Despite being dominated by "soft corals", the order Alcyonacea now contains all species known as "gorgonian corals", that produce a hard skeleton made from gorgonin, a protein unique to the group that makes their skeletons quite different from "true" corals ( Scleractinia). These "gorgonion corals" can be found in suborders Holaxonia, Scleraxonia, and Stolonifera. Many soft corals are easily collected in the wild for the reef aquarium hobby, as small cuttings are less prone to infection or damage during shipping than stony corals. Nevertheless, home-grown specimens tend to be more adaptable to aquarium life and help conserve wild reefs. Soft corals grow quickly in captivity and are easily divided into new individuals, and so those grown by aquaculture are often hardier and less expensive than imported corals from the wild.

Ecology

Each gorgonian polyp has eight tentacles, which catch

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

and particulate matter for consumption. This process, called filter feeding, is facilitated when the "fan" is oriented across the prevailing current to maximise water flow to the gorgonian, hence food supply. Some gorgonians contain algae, or zooxanthellae. This symbiotic relationship assists in giving the gorgonian nutrition by

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

. Gorgonians possessing zooxanthellae are usually characterized by brownish polyps. Gorgonians are found primarily in shallow waters, though some have been found at depths of several thousand feet. The size, shape, and appearance of gorgonians can be correlated with their location. The more fan-shaped and flexible gorgonians tend to populate shallower areas with strong currents, while the taller, thinner, and stiffer gorgonians can be found in deeper, calmer waters. Other fauna, such as hydrozoa,

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

, and brittle stars, are known to dwell within the branches of gorgonian colonies. The pygmy seahorse not only makes certain species of gorgonians its home, but also closely resembles its host, thus is well camouflaged. Two species of pygmy seahorse, '' Hippocampus bargibanti'' and '' Hippocampus denise,'' are obligate residents on gorgonians. ''H. bargibanti'' is limited to two species in the single genus ''Muricella''. Gorgonians produce unusual

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s in their tissues, particularly diterpenes, and some of these are important candidates for new drugs. These compounds may be part of the chemical defenses produced by gorgonians to render their tissue distasteful to potential predators. Bottlenose dolphins in the

Red Sea The Red Sea is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

have been observed swimming against these tissues, in what is thought to be an attempt to take advantage of the antimicrobial qualities of diterpenes. Despite these chemical defenses, the tissues of gorgonians are prey for flamingo tongue snails of the genus '' Cyphoma,''

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have b ...

s, the fireworm ''Hermodice'' spp., and their polyps are food for butterflyfishes. Amongst the nudibranchs which feed on soft corals and sea fans are the

Tritoniidae Tritoniidae is a taxonomic family of nudibranchs in the suborder Cladobranchia, shell-less marine gastropod molluscs.MolluscaBase (2018)Tritoniidae Lamarck, 1809.Accessed on 2021-01-01 This family includes some of the largest known nudibranch ...

and the genus '' Phyllodesmium'' which specialises in eating '' Xenia'' species.

Suborders and families

The World Register of Marine Species lists these suborders and families: * suborder Alcyoniina ** family Acrophytidae McFadden & Ofwegen, 2017 ** family Alcyoniidae Lamouroux, 1812 ** family Aquaumbridae Breedy, van Ofwegen & Vargas, 2012 ** family Corymbophytidae McFadden & Ofwegen, 2017 ** family Leptophytidae McFadden & Ofwegen, 2017 ** family Nephtheidae Gray, 1862 ** family Nidaliidae Gray, 1869 ** family Paralcyoniidae Gray, 1869 ** family Xeniidae Ehrenberg, 1828 * suborder Calcaxonia ** family Chrysogorgiidae Verrill, 1883 ** family Ellisellidae Gray, 1859 ** family Ifalukellidae Bayer, 1955 ** family Isididae Lamouroux, 1812 ** family Primnoidae Milne Edwards, 1857 * suborder Holaxonia ** family Acanthogorgiidae Gray, 1859 ** family Dendrobrachiidae Brook, 1889 ** family Gorgoniidae Lamouroux, 1812 ** family Keroeididae Kinoshita, 1910 ** family Plexauridae Gray, 1859 * suborder Protoalcyonaria ** family Taiaroidae Bayer & Muzik, 1976 * suborder Scleraxonia ** family Anthothelidae Broch, 1916 ** family Briareidae Gray, 1859 ** family Coralliidae Lamouroux, 1812 ** family Melithaeidae Gray, 1870 ** family Paragorgiidae Kükenthal, 1916 ** family Parisididae Aurivillius, 1931 ** family Spongiodermidae Wright & Studer, 1889 ** family Subergorgiidae Gray, 1859 ** family Victorgorgiidae Moore, Alderslade & Miller, 2017 * suborder Stolonifera ** family Acrossotidae Bourne, 1914 ** family Arulidae McFadden & van Ofwegen, 2012 ** family Clavulariidae Hickson, 1894 ** family Coelogorgiidae Bourne, 1900 ** family Cornulariidae Dana, 1846 ** family Pseudogorgiidae Utinomi & Harada, 1973 ** family Tubiporidae Ehrenberg, 1828 * family Acanthoaxiidae van Ofwegen & McFadden, 2010 * family Haimeidae Wright, 1865 * family Paramuriceidae Bayer, 1956 * family Parasphaerascleridae McFadden & van Ofwegen, 2013 * family Viguieriotidae File:Alcyonium acaule Marion, 1878 3.jpg, '' Alcyonium acaule'', an alcyoniid File:Dendronephthya hemprichi at Gilli Lawa Laut.JPG, '' Dendronephthya hemprichi'', a nephtheid File:Siphonogorgia godeffroyi (Pink soft coral).jpg, '' Siphonogorgia godeffroyi'', a nidaliid File:Maasella edwardsi (de Lacaze-Duthiers, 1888).jpg, '' Maasella edwardsi'', a paralcyoniid File:Pulsating xenid, Heteroxenia fuscescens, a soft coral that pulsates rhythmically around 40 times a minute (6163181047).jpg, '' Heteroxenia fuscescens'', a xeniid File:Iridigorgia sp.jpg, '' Iridigorgia'' sp., a chrysogorgiid File:Sea Whip (Ellisella sp.) (8486549324).jpg, '' Ellisella'' sp., an ellisellid File:Isidella tentaculum - NOAA.jpg, '' Isidella tentaculum'', an isidid File:Plumarella pellucida.jpg, '' Plumarella pellucida'', a primnoid File:Pygmy Seahorse -Lembeh Straits.jpg, '' Muricella'' sp., an acanthogorgiid File:Gorgonia ventalina, Bahamas.jpg, '' Gorgonia ventalina'', a gorgoniid File:Paramuricea clavata (Risso, 1826) 5.jpg, '' Paramuricea clavata'', a paramuriceid File:Muricea elongata.jpg, '' Muricea elongata'', a plexaurid File:Anthothela grandiflora.jpg, '' Anthothela grandiflora'', an anthothelid File:Briareum 2.JPG, '' Briareum'' sp., a briareid File:Corallium rubrum (Linnaeus, 1758) 11.jpg, '' Corallium rubrum'', a coralliid File:Acabaria splendens.jpg, '' Acabaria splendens'', a melithaeid File:Expl0924 - Flickr - NOAA Photo Library.jpg, '' Paragorgia arborea'', a paragorgiid File:Gorgone de Mayotte.jpg, '' Annella mollis'', a subergorgiid File:Pachiclavularia viridis.JPG, '' Clavularia viridis'', a clavulariid File:Cornularia cornucopiae.jpg, '' Cornularia cornucopiae'', a cornulariid File:Tubipora purpurea-Musée zoologique de Strasbourg.jpg, ''

Tubipora musica The organ pipe coral (''Tubipora musica'') is an alcyonarian Octocorallia, octocoral native to the waters of the Indian Ocean and the central and western regions of the Pacific Ocean. It is the Monotypic, only known species of the genus ''Tubipor ...

'', Tubiporidae File:Iciligorgia schrammi.jpg, '' Iciligorgia schrammi''

References

External links

The Marine Fauna Gallery of Norway

Gorgonian Corals
{{Authority control Octocorallia Anthozoan orders