Alcyonacea, or soft corals, are an order of

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

s. In addition to the fleshy soft corals, the order Alcyonacea now contains all species previously known as "gorgonian corals", that produce a more or less hard skeleton, though quite different from "true" corals (

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a ...

). These can be found in suborders

Holaxonia Holaxonia is a suborder of soft corals, a member of the phylum Cnidaria.Holaxonia
World Regis ...

Scleraxonia Scleraxonia is a suborder of corals, a member of the phylum Cnidaria. Characteristics Members of Scleraxonia have a skeletal axis made of calcified spicules, organic fibres or both, which may be separate, linked or fused together. Families and ...

, and

Stolonifera Stolonifera is a suborder of soft corals in the order Alcyonacea. Members of this taxon are characterised by having separate polyps budding off an encrusting horizontal, branching stolon. The skeletons include spicules or consists of a horny exte ...

. They are

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...

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. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referr ...

and subtropics. 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 state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

Bermuda ) , anthem = "God Save the King" , song_type = National song , song = "Hail to Bermuda" , image_map = , map_caption = , image_map2 = , mapsize2 = , map_caption2 = , subdivision_type = Sovereign state , subdivision_name = , es ...

, 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 Paleoclimatology (American and British English spelling differences, British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the ...

and

paleoceanography Paleoceanography is the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation and biological productivity. Paleoceanographic studies using environment models ...

, as their skeletal growth rate and composition are highly correlated with seasonal and climatic variation.

Features

Soft corals contain minute, spiny skeletal elements called

sclerite A sclerite (Greek , ', meaning " hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...

s, 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 ''Sinularia'' is a genus of soft coral in the family Alcyoniidae. They are commonly known as leather corals and currently have 166 described species In biology, a species is the basic unit of classification and a taxonomic rank of an o ...

'' are able to cement sclerites and consolidate them at their base into alcyonarian spiculite, thus making them reef builders. Unlike

stony coral Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a mo ...

s, most soft corals thrive in nutrient-rich waters with less intense light. Almost all use symbiotic photosynthetic

zooxanthella Zooxanthellae is a colloquial term for single-celled dinoflagellates that are able to live in symbiosis with diverse marine invertebrates including demosponges, corals, jellyfish, and nudibranchs. Most known zooxanthellae are in the genus '' Sym ...

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 (

). These "gorgonion corals" can be found in suborders Holaxonia, Scleraxonia, and

. 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

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work ma ...

s, which catch

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

and particulate matter for consumption. This process, called

filter feeding Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

, 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

e. This symbiotic relationship assists in giving the gorgonian nutrition by

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. 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 Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialize ...

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

, and

brittle stars Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomo ...

, are known to dwell within the branches of gorgonian colonies. The

pygmy seahorse The pygmy seahorses comprise several species of tiny seahorse in the syngnathid family (biology), family or Syngnathidae (seahorses and pipefish). Family Syngnathidae is part of order Syngnathiformes, which contains fishes with fused jaws that su ...

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 ''Hippocampus denise'', also known as Denise's pygmy seahorse or the yellow pygmy seahorse, is a seahorse of the family Syngnathidae native to the western Pacific. Description Denise's pygmy seahorse is a small fish which can reach a maximum l ...

,'' are obligate residents on gorgonians. ''H. bargibanti'' is limited to two species in the single genus ''Muricella''. Gorgonians produce unusual

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...

s in their tissues, particularly

diterpene Diterpenes are a class of chemical compounds composed of four isoprene units, often with the molecular formula C20H32. They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway, with geranylgeranyl pyrophosphate being ...

s, and some of these are important candidates for new drugs. These compounds may be part of the

chemical defense Chemical defense is a life history strategy employed by many organisms to avoid consumption by producing toxic or repellent metabolites or chemical warnings which incite defensive behavioral changes. The production of defensive chemicals occurs in ...

s produced by gorgonians to render their tissue distasteful to potential predators. Bottlenose dolphins in the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...

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 ''Cyphoma'' is a genus of predatory tropical sea snails, a taxonomic group of marine gastropod molluscs in the family Ovulidae, a family which is sometimes known as the false cowries or cowry allies. Distribution Cyphoma snails live in tropic ...

,''

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...

s, the fireworm ''Hermodice'' spp., and their polyps are food for

butterflyfish The butterflyfish are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. The approximately 129 species in 12 genera are found mostly on the reefs of the Atla ...

es. 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 nudibranchs, ...

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

Suborders and families

The World Register of Marine Species lists these suborders and

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...

: * 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 Xeniidae is a family of soft coral in the order Alcyonacea. Predators Predatory sea slugs of the genus '' Phyllodesmium'' are reported to feed on Xeniidae species. Representatives of this family have been observed to provide shelter to juvenil ...

Ehrenberg, 1828 * suborder Calcaxonia ** family Chrysogorgiidae Verrill, 1883 ** family Ellisellidae Gray, 1859 ** family Ifalukellidae Bayer, 1955 ** family

Isididae Bamboo coral, family Isididae, is a family of mostly deep-sea coral of the phylum Cnidaria. It is a commonly recognized inhabitant of the deep sea, due to the clearly articulated skeletons of the species. Deep water coral species such as this ...

Lamouroux, 1812 ** family

Primnoidae Primnoidae is a family (biology), family of Alcyonacea, soft corals. Genera The World Register of Marine Species includes the following Genus, genera in the family: *''Abyssoprimnoa'' Cairns, 2015 *''Acanthoprimnoa'' Cairns & Bayer, 2004 *''Ag ...

Milne Edwards, 1857 * suborder

Holaxonia Holaxonia is a suborder of soft corals, a member of the phylum Cnidaria.Holaxonia
World Regis ...

** family Acanthogorgiidae Gray, 1859 ** family Dendrobrachiidae Brook, 1889 ** family Gorgoniidae Lamouroux, 1812 ** family Keroeididae Kinoshita, 1910 ** family

Plexauridae Plexauridae is a family of marine colonial octocorals in the phylum Cnidaria. Members of this family are found in shallow tropical and subtropical seas. Many species contain symbiotic photosynthetic protists called zooxanthellae. Characteristi ...

Gray, 1859 * suborder

Protoalcyonaria ''Taiaroa'' is a genus of deep-water, solitary marine octocorals in the family Taiaroidae. ''Taiaroa'' is monotypic in the family Taiaroidae and contains a single species, ''Taiaroa tauhou''. The species was first described by the marine zoologis ...

** family Taiaroidae Bayer & Muzik, 1976 * suborder

** family Anthothelidae Broch, 1916 ** family

Briareidae Briareidae is a family of corals, a member of the phylum Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter ...

Gray, 1859 ** family

Coralliidae Coralliidae, also known as precious corals, is a taxonomic family of soft corals belonging to the phylum Cnidaria of the family Scleraxonia. These sessile corals are one of the most dominant members of hard-bottomed benthic environments such as ...

Lamouroux, 1812 ** family Melithaeidae Gray, 1870 ** family Paragorgiidae Kükenthal, 1916 ** family

Parisididae ''Parisis'' is a genus of corals in the monotypic family Parisididae. Species Species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often ...

Aurivillius, 1931 ** family Spongiodermidae Wright & Studer, 1889 ** family Subergorgiidae Gray, 1859 ** family Victorgorgiidae Moore, Alderslade & Miller, 2017 * suborder

** family Acrossotidae Bourne, 1914 ** family

Arulidae Arulidae is a family of corals belonging to the order Alcyonacea. Genera: * ''Arula'' McFadden & van Ofwegen, 2012 * ''Bunga Bunga may refer to * Bunga mas, a tribute that was sent every three years to the King of Siam from its vassal states in t ...

McFadden & van Ofwegen, 2012 ** family Clavulariidae Hickson, 1894 ** family Coelogorgiidae Bourne, 1900 ** family Cornulariidae Dana, 1846 ** family

Pseudogorgiidae ''Pseudogorgia'' is a monotypic genus of corals Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important ...

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 ''Ellisella'', commonly known as sea whip, is a Genus (biology), genus of soft coral in the Family (biology), family Ellisellidae. ''Ellisella'' constitutes like bushy shrub gorgonians which dominant color is brown to reddish and polyps are whi ...

'' 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 ''Gorgonia ventalina'', the common sea fan and purple sea fan, is a species of sea fan, an octocoral in the family Gorgoniidae. It is found in the western Atlantic Ocean and the Caribbean Sea. Description ''G. ventalina'' is a fan-shaped col ...

'', a gorgoniid File:Paramuricea clavata (Risso, 1826) 5.jpg, ''

Paramuricea clavata ''Paramuricea clavata'', the violescent sea-whip, is a species of colonial soft coral in the family Plexauridae. It is found in shallow seas of the north-eastern Atlantic Ocean and the north-western Mediterranean Sea as well as Ionian Sea. This s ...

'', 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 Precious coral, or red coral, is the common name given to a genus of marine corals, ''Corallium''. The distinguishing characteristic of precious corals is their durable and intensely colored red or pink-orange skeleton, which is used for m ...

'', a coralliid File:Acabaria splendens.jpg, '' Acabaria splendens'', a melithaeid File:Expl0924 - Flickr - NOAA Photo Library.jpg, ''

Paragorgia arborea ''Paragorgia arborea'' is a species of coral in the family Paragorgiidae, commonly known as the bubblegum coral because of its bulbous branch tips. It mainly grows in depths between at temperatures between . It is found widespread in the Nort ...

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

References

External links

The Marine Fauna Gallery of Norway

Gorgonian Corals
{{Taxonbar, from=Q137552, from2=Q1365073 Octocorallia Cnidarian orders