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Isastrea
|genus_authority=Milne-Edwards & Haime, 1851〔(【引用サイトリンク】 title=''Isastrea'' )〕|ordo=Scleractinia|image=Isastrea richardsoni.jpg|image_caption=''I. richardsoni'' showing calyces at various levels of magnification}}
''Isastrea'' is an extinct genus of coral which lived during the Jurassic and Cretaceous. Its fossils have been found in Europe, Africa, and North America.〔
==Description==
''Isastrea'' belonged to a group known as the hexacorals, so named for the shape of each individual polyp skeleton (corallite).〔 Each corallite was between and in diameter. In addition, 30–80 septa (walls dividing body cavities) were present in each animal.〔 Its walls were "weak, discontinuous or absent". In some species, adjacent septa would fuse. Dissepiments ("small blistery plates" serving the purpose of internal support) were plentiful in the animal. Columella (central "rod- or plate-like" structures) were present as well, but were not very strong. The genus is believed to have lived in colonies (each of which could have been long) and formed coral reefs.〔 The colonies were "massive",〔 "encrusting, platey, dome-shaped or sometimes ramose".〔 It was a hermatypic coral, which require "warm, clear, shallow water" and live in symbiotic relationships with algae.〔 It is also likely that zooxanthellae (a kind of protozoa) lived on the coral.〔 It has been theorized that ''Isastrea'' could endure lower temperatures than most other hermatypic corals because it occurs farther north than them.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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