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Anthozoa (sea-anemones, corals, sea pens; phylum Cnidaria) A class of exclusively polyploid, marine cnidarians. They probably first appeared in the Ordovician although there are possible records for some groups in the Cambrian. They are solitary or colonial and usually sedentary. The oral end is expanded as an oral disc with a central mouth that has one or more rings of hollow tentacles. Anthozoans have a well-developed stomodeum (gullet) leading from the mouth to the enteron (gastrovascular cavity). The interior of the enteron is divided by mesenteries (infoldings of the gut wall). Those members of the class that secrete hard, calcareous skeletons are important in the geologic record from the Palaeozoic onwards, and at some levels form true coral reefs. In the Palaeozoic they are often associated with other organisms, e.g. stromatoporoids (Stromatoporoidea), to produce organic build-ups or reef mounds. See HETEROCORALLIA; OCTOCORALLIA; RUGOSA; SCLERACTINIA; TABULATA; and ZOANTHARIA.
Anthozoa (Actinozoa; sea anemones, corals, sea pens; phylum Cnidaria) A class of exclusively polypoid, marine cnidarians that are solitary or colonial, and usually sedentary. The oral end is expanded as an oral disc with a central mouth, with one or more rings of hollow tentacles. A well-developed stomodaeum leads from the mouth to a gastrovascular cavity, generally with one or two vertical grooves. The gastrovascular cavity is partitioned into compartments by complete or incomplete mesenteries, some bearing endodermal gonads. Anthozoans first appeared in the Ordovician.