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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 mouth is fringed with tentacles. Although some species are solitary, most are colonial.
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).
There are two main classifications for corals: hard coral (scleractinian and stony coral) [13] which form reefs by a calcium carbonate base, with polyps that bear six stiff tentacles, [14] and soft coral (Alcyonacea and ahermatypic coral) [13] which are pliable and formed by a colony of polyps with eight feather-like tentacles. [14]
Octocorallia (also known as Alcyonaria) is a class of Anthozoa comprising over 3,000 species [1] of marine organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians (sea fans and sea whips) within three orders: Alcyonacea, Helioporacea, and Pennatulacea. [2]
Anthozoans are exclusively marine, and include sea anemones, stony corals, soft corals, sea pens, sea fans and sea pansies. Anthozoa is the largest taxon of cnidarians; over six thousand solitary and colonial species have been described. They range in size from small individuals less than half a centimetre across to large colonies a metre or ...
The polyps that live inside this bark are less than 2 mm (0.0787 in) [12] and are gelatinous and have six tentacles (the same as hard corals and unlike soft corals, which have eight). [13] These polyps can be nearly any color. [3] Some corals also have "sweeper tentacles", which can grow up to 15 mm (0.591 in) long. [12]
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.
Instead it refers most commonly to the hardened parts of arthropod exoskeletons and the internal spicules of invertebrates such as certain sponges and soft corals. In paleontology , a scleritome is the complete set of sclerites of an organism, often all that is known from fossil invertebrates.