The hexacoral order Zoantharia is characterised by two rows of tentacles and, most often, a colonial mode of life. This order is commonly referred as “zoanthids” in English despite the possible confusion with the family Zoanthidae, a group within this order, restricted to shallow tropical and subtropical environments. Here, we follow the most used standards in past and present specialised taxonomic literature, using Zoantharia as the scientific order name and “zoanthids” as the common name for the order.
Zoanthids can be found in most marine environments although very little is known of their ecological role in the ecosystem.
Deep-sea zoanthids remain largely unknown with the exception of a few species regularly dredged or trawled on deep-sea soft sediments. Most of these zoanthids belong to the genus Epizoanthus Gray, 1867, in the family Epizoanthidae Delage and Hérouard, 1901, with a few species associated with pagurids  and some associated with hexactinellid sponge stalks.
Isozoanthus Carlgren in Chun, 1903 within the family Parazoanthidae Delage and Hérouard, 1901 is the second most speciose genus of deep-sea zoanthid species, (however recent taxonomic work casts doubt on the status of this genus ).
Another group of deep-sea zoanthids was recently described from over 3000 m depth in a cold seep environment, the family Abyssoanthidae Reimer and Fujiwara in Reimer et al., 2007. Recently specimens belonging to this group have been found in other bathyal and abyssal environments around the world , .
Between 100 m and 2000 m depth, numerous epizoic zoanthids, usually belonging to the family Parazoanthidae, can be found. However, most of them remain undescribed despite some species such as the Hawaiian gold coral (often referred as Gerardia) having been known for decades.
Table 1 reviews the currently recognised zoanthid genera and families with an indication of the genera found in the deep-sea.
Table 1. Classical taxonomic organisation within the order Zoantharia.doi:10.1371/journal.pone.0052607.t001
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