Octocorallia

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Octocorallia, along with Hexacorallia, is one of the two extant classes of Anthozoa.[1] It comprises over 3,000 species of marine and brackish animals consisting of colonial polyps with 8-fold symmetry, commonly referred informally as "soft corals". It was previously known by the now unaccepted scientific names Alcyonacea[2] and Gorgonacea,[3] both deprecated c. Template:TrimScript error: No such module "Check for unknown parameters"., and by the also deprecated name of Alcyonaria, in earlier times.[4][5]

Its only two orders are Malacalcyonacea and Scleralcyonacea, which include corals such as those under the common names of blue corals, sea pens, and gorgonians (sea fans and sea whips).[4] These animals have an internal skeleton secreted by their mesoglea, and polyps with tipically eight tentacles and eight mesenteries. As is the case with all cnidarians, their complex life cycle includes a motile, planktonic phase (a larva called planula), and a later characteristic sessile phase.

Octocorals have existed at least since the Ordovician period, as shown by Maurits Lindström's findings in the 1970s.[6] A 2023 work suggested that the Cambrian fossil Pywackia may represent a Cambrian octocoral,[7][8][9] and molecular techniques have even pointed to a Precambrian origin for Octocorallia. For instance, a 2021 study built a time-calibrated phylogenetic tree that has placed the origin of Octocorallia in the Ediacaran (578 Mya).[10]

Biology

File:Tubipora01.jpg
Full corallum of Tubipora musica.

Octocorals resemble the stony corals in general appearance and in the size of their polyps, but lack the distinctive stony skeleton. Also unlike the stony corals, each polyp has only eight tentacles, each of which is feather-like in shape, with numerous side-branches, or pinnules.

Octocorals are colonial organisms, with numerous tiny polyps embedded in a soft matrix that forms the visible structure of the colony. The matrix is composed of mesogleal tissue, lined by a continuous epidermis and perforated by numerous tiny channels. The channels interconnect the gastrovascular cavities of the polyps, allowing water and nutrients to flow freely between all the members of the colony. The skeletal material, called coenenchyme, is composed of living tissue secreted by numerous wandering amoebocytes. Although it is generally soft, in many species it is reinforced with calcareous or horny material.[11]

The polyp is largely embedded within the colonial skeleton, with only the uppermost surface, including the tentacles and mouth, projecting about the surface. The mouth is slit-like, with a single ciliated groove, or siphonoglyph, at one side to help control water flow. It opens into a tubular pharynx that projects down into a gastrovascular cavity that occupies the hollow interior. The pharynx is surrounded by eight radial partitions, or mesenteries, that divide the upper part of the gastrovascular cavity into chambers, one of which connects to the hollow space inside each tentacle. The gonads are located near the base of each mesentery.[11] Octocorals have high phenotypic plasticity from adapting to dynamic environments where temperature, pH, and other parameters are in constant flux[12] and have shown high recruitment rates post-die-off events caused by El Niño events.[13]

Bioluminescence is found in 32 genera, a trait estimated to have evolved 540 million years ago, the earliest timing of emergence of bioluminescence in the marine environment.[14]

Phylogeny

Octocorallia is considered to be monophyletic, meaning that all contained species are descended from a common ancestor, but the relationships between subdivisions are not well known. The sea pens (Pennatulacea) and blue coral (Helioporacea) continue to be assigned separate orders, whereas the current order Alcyonacea was historically represented by four orders: Alcyonacea, Gorgonacea, Stolonifera and Telestacea.

Unplaced taxa

The following taxa are unplaced within Octocorallia according to the World Register of Marine Species since April 2024Template:Dated maintenance category (articles)Script error: No such module "Check for unknown parameters".:[15]

Families:

  • Haimeidae Wright, 1865Script error: No such module "Check for unknown parameters".
  • Pseudogorgiidae Utinomi & Harada, 1973Script error: No such module "Check for unknown parameters".

Genera:

  • Aspera Dautova, 2018Script error: No such module "Check for unknown parameters".
  • Bayergorgia Williams & López-González, 2005Script error: No such module "Check for unknown parameters".
  • Briareopsis Bayer, 1993Script error: No such module "Check for unknown parameters".
  • Caliacis Deichmann, 1936Script error: No such module "Check for unknown parameters".
  • Canarya Ocaña & van Ofwegen, 2003Script error: No such module "Check for unknown parameters".
  • Ceratocaulon Jungersen, 1892Script error: No such module "Check for unknown parameters".
  • Chalcogorgia Bayer, 1949Script error: No such module "Check for unknown parameters".
  • Chondronephthya Utinomi, 1960Script error: No such module "Check for unknown parameters".
  • Daniela von Koch, 1891Script error: No such module "Check for unknown parameters".
  • Denhartogia Ocaña & van Ofwegen, 2003Script error: No such module "Check for unknown parameters".
  • Distichogorgia Bayer, 1979Script error: No such module "Check for unknown parameters".
  • Elasmogorgia Wright & Studer, 1889Script error: No such module "Check for unknown parameters".
  • Flagelligorgia Cairns & Cordeiro, 2017Script error: No such module "Check for unknown parameters".
  • Hypnogorgia Duchassaing & Michelotti, 1864Script error: No such module "Check for unknown parameters".
  • Inflatocalyx Verseveldt & Bayer, 1988Script error: No such module "Check for unknown parameters".
  • Lanthanocephalus Williams & Starmer, 2000Script error: No such module "Check for unknown parameters".
  • Lignopsis Pérez & Zamponi, 2000Script error: No such module "Check for unknown parameters".
  • Mesogligorgia López-González, 2007Script error: No such module "Check for unknown parameters".
  • Moolabalia Alderslade, 2001Script error: No such module "Check for unknown parameters".
  • Pseudocladochonus Versluys, 1907Script error: No such module "Check for unknown parameters".
  • Pseudosuberia Kükenthal, 1916Script error: No such module "Check for unknown parameters".
  • Pseudothesea Kükenthal, 1919Script error: No such module "Check for unknown parameters".
  • Rhipiopathes
  • Rolandia de Lacaze-Duthiers, 1900Script error: No such module "Check for unknown parameters".
  • Scleranthelia Studer, 1878Script error: No such module "Check for unknown parameters".
  • Speirogorgia Williams, 2019Script error: No such module "Check for unknown parameters".
  • Sphaeralcyon López-González & Gili, 2000Script error: No such module "Check for unknown parameters".
  • Stereacanthia Thomson & Henderson, 1906Script error: No such module "Check for unknown parameters".
  • Stereogorgia Kükenthal, 1916Script error: No such module "Check for unknown parameters".
  • Stereosoma Hickson, 1894Script error: No such module "Check for unknown parameters".
  • Tesseranthelia Bayer, 1981Script error: No such module "Check for unknown parameters".
  • Thelogorgia Bayer, 1991Script error: No such module "Check for unknown parameters".
  • Tubigorgia Pasternak, 1985Script error: No such module "Check for unknown parameters".
  • Verseveldtia Williams, 1990Script error: No such module "Check for unknown parameters".
  • Williamsium Moore, Alderslade & Miller, 2017Script error: No such module "Check for unknown parameters".
  • Xenogorgia Bayer & Muzik, 1976Script error: No such module "Check for unknown parameters".

References

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External links

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