Holaxonia
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| Holaxonia | |
|---|---|
 | |
| Pinnigorgia sp. | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Cnidaria |
| Subphylum: | Anthozoa |
| Class: | Octocorallia |
| Order: | Alcyonacea |
| Suborder: | Holaxonia Studer, 1887 |
| Families | |
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See text | |
Holaxonia (English name: holaxonians[1]) is a former Octocorallian suborder of the order Gorgonacea (English names: gorgonians or sea fans), or alternatively of the broadly conceived order Alcyonacea. Before 1981/1999, Holaxonia usually also included the taxon Calcaxonia (informal name: restricted Holaxonia).[2][3][4][5]
Since a 2022 revision of the Octocorallia, the content of the former Holaxania has been included in the new order Malacalcyonacea, within which it does not form a monophyletic group (clade) and has no name. The two Holaxonian genera Dendrobrachia a Ideogorgia are an exception in that they have been included not in the order Malacalcyonacea, but in the order Scleralcyonacea.[6]
Vernacular names of certain members of Holaxonia include: sea fan, sea whip, sea rod, and sea blade.
Members of Holaxonia are soft corals. They are colonial, sessile organisms and are generally tree-like in structure. They do not have a hard skeleton composed of calcium carbonate but have a firm but pliable, central axial skeleton composed of a fibrous protein called gorgonin embedded in a tissue matrix, the coenenchyme. In some genera this is permeated with a calcareous substance in the form of fused spicules. Members of Holaxonia are characterized by having an unspiculated axis and often a soft, chambered central core.[7] The polyps have eight-fold symmetry and in many species, especially in the families Gorgoniidae and Plexauridae, contain symbiotic photosynthetic algae called zooxanthellae. These soft corals are popular in salt water aquaria.[8][9]