Hexacorallia

Hexacorallia; Temporal range: Fortunian–Present PreꞒ Ꞓ O S D C P T J K Pg N
	A stony coral, Acropora latistella
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Cnidaria
Subphylum:	Anthozoa
Class:	Hexacorallia; Haeckel, 1896
Orders
	See text.

Hexacorallia is a class 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, and zoanthids, arranged within five extant orders.^[2] The hexacorallia are distinguished from another class of Anthozoa, Octocorallia, in having six or fewer axes of symmetry in their body structure; the tentacles are simple and unbranched and normally number more than eight.^[3] 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 order of rugose corals.

Phylogeny

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, Antipatharia was considered to be in a separate class called Ceriantipatharia, though more recent genetic studies place it in Hexacorallia.^[2]

The class includes important coral reef builders such as the stony corals, sea anemones, and zoanthids. The recognized orders are shown below:^[4]

Actiniaria – sea anemones
Antipatharia – black corals
Corallimorpharia – corallimorpharians aka "false corals"
†Rugosa – rugose corals
Scleractinia – stony corals
†Tabulata – tabular corals
Zoantharia – zoanthids

References

^ Han, Jian; Kubota, Shin; Uchida, Hiro-omi; Stanley Jr., George D.; Yao, Xiaoyong; Shu, Degan; Li, Yong; Yasui, Kinya (October 13, 2010). "Tiny Sea Anemone from the Lower Cambrian of China". PLOS One. 5 (10): e13276. Bibcode:2010PLoSO...513276H. doi:10.1371/journal.pone.0013276. PMC 2954142. PMID 20967244.
^ ^a ^b 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". Zootaxa. 1668: 1–766. doi:10.11646/zootaxa.1668.1.11. hdl:1808/13641. ISSN 1175-5326.
^ Light. Sol Felty (2007). The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon. University of California Press. p. 177. ISBN 978-0-520-23939-5.
^ "WoRMS - World Register of Marine Species - Hexacorallia". marinespecies.org. Retrieved 2018-04-03.