Scleractinia

Scleractinia, also called stony corals or hard corals, an order in the Cnidaria. It contains the polyps which build most coral reefs.

Stony corals
Scleractinian corals, illustration by Ernst Haeckel, 1904
Scientific classification
Unrecognized taxon (fix):	Scleractinia
Families
About 35, see text.
Synonyms
Madreporaria

Most of these corals are colonial. They secrete calcium carbonate, the base of every reef. Very often, the corals form a symbiosis with unicellular dinoflagellates. These zooxanthellae are usually of the genus Symbiodinium.

The closest relatives to stony corals are the sea anemones. Stony corals are only distantly related to fire corals and soft corals. There are about 1500 species, in 35 families.

Scleractinia Media

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  Diploria labyrinthiformis, a brain coral

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  Meandering corallite walls of an intratentacular budding coral

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  Separate corallites of an extratentacular budding species

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  Settlement and early life stages of scleractinian corals. This figure highlights on the first steps of a coral larvae (searching, attachment, and metamorphosis) toward an adult coral.

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  Montastraea annularis can be fragmented to form new colonies.

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  Palaeozoic rugose corals with calcite skeletons, like this Grewingkia canadensis, are doubtfully ancestors of the Scleractinia.

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  Scleractinian coral from the Matmor Formation (Jurassic) of Makhtesh Gadol

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  A deep-sea Madreporaria collected by the Royal Indian Marine Survey ship Investigator, 1898

References

Polyps of hard coral Favites come out at night to feed