Hexacorallia

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Hexacorallia
Acropora latistella (Table coral).jpg
A stony coral, Acropora latistella
Scientific classification e
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Subclass: Hexacorallia
Orders
Aspidiscus cristatus from the Cenomanian (Upper Cretaceous) of southern Israel; oral view.
Aspidiscus cristatus from the Cenomanian (Upper Cretaceous) of southern Israel; aboral view.

Hexacorallia is a subclass of Anthozoa comprising approximately 4,300 species of aquatic organisms formed of polyps, generally with 6-fold symmetry. It includes all of the stony corals, most of which are colonial and reef-forming, as well as all sea anemones, tube anemones, and zoanthids, ranged within six extant orders.[1] The hexacorallia are distinguished from the other subclass of Anthozoa, Octocorallia, in having six or fewer axes of symmetry in their body structure and only single rows[citation needed] of tentacles. These organisms are formed of individual soft polyps which in some species live in colonies and can secrete a calcite skeleton. As with all Cnidarians, these organisms have a complex life cycle including a motile planktonic phase and a later characteristic sessile phase. Hexacorallia also include the significant extinct orders of the rugose corals and tabulate corals

Phylogeny[edit]

Hexacorallia is considered to be monophyletic, that is all contained species are descended from a common ancestor, however it has been suggested that many of the current orders are not. Historically Ceriantharia and Antipatharia were considered to be a separate subclass called Ceriantipatharia, though more recent genetic studies place them in Hexacorallia with Ceriantharia as the oldest, or basal, group.[1]

The subclass includes important coral reef builders the stony corals (Scleractinia), sea anemones (Actiniaria) and related tube-dwelling anemones (Ceriantharia), and zoanthids (Zoantharia). Antipatharia contains the black corals and Corallimorpharia are similar to anemones. The extant orders are shown below:[1]

 Hexacorallia 

Ceriantharia




Actiniaria



Antipatharia



Corallimorpharia



Scleractinia



Zoantharia




The anemone-like Relicanthus daphneae was classified as incerti ordinis within this class in May 2014.

A number of extinct orders of corals have been classified as their calcium skeleton forms a prolific fossil record. These are generally thought to be close to the ancestors of modern Scleractinians and existed during the Paleozoic Era 541-242 million years ago:[2][3]

  • Numidiaphyllida †
  • Kilbuchophyllida †
  • Heterocorallia †
  • Rugosa
  • Heliolitida †
  • Tabulata
  • Cothoniida †
  • Tabuloconida †

References[edit]

  1. ^ a b c Daly, M.; Brugler, M.P., Cartwright, P., Collins, A.G., Dawson, M.N., Fautin, D.G., France, S.C., McFadden, C.S., Opresko, D.M., Rogriguez, E., Romano, S.L. & Stake, J.L. (2007-07-21). "The phylum Cnidaria: A review of phylogenetic patterns and diversity 300 years after Linnaeus" (PDF). Zootaxa 1668: 1–766. ISSN 1175-5326. 
  2. ^ Oliver, W. A., Jr. (1996). "Origins and relationships of Paleozoic coral groups and the origin of the Scleractinia". In G. D. J. Stanley (ed.). Paleobiology and Biology of Corals. Columbus, Ohio: The Paleontological Society. pp. 107–134. 
  3. ^ Ben Kotrc (2005). "Anthozoa: Subgroups". Fossil Groups. University of Bristol. Retrieved 2009-03-23. 

External links[edit]