Among the more familiar corals are the gorgonian, or horny, corals of the order Gorgonacea. This group includes corals commonly known as sea feathers, sea fans, and the red coral (genus Corallium) often used in jewellery. Members of the gorgonian coral group are often present in reefs. The body consists of an erect central rod of organic material called gorgonin, surrounded by a cylinder of calcareous spicules and by the polyp organisms, in branching, plant-like forms.
The spicules contain a pigment that gives the gorgonian an orange or purple colour. Yellow or brown colours may be caused by zooxanthellae. In Corallium, the red jewellery coral, the central rod of gorgonin is replaced by a solid rod of fused red calcareous spicules that can be polished.
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