Calcaxonia

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Calcaxonia was an informal name used from 1981 to 1999 for a group of octocorals, sometimes called “restricted Holaxonia.” It was usually treated as part of Holaxonia within the octocorals, until 1999 when it was formally defined as its own suborder.

In 2022, scientists revised octocoral classification and placed Calcaxonia in a new order called Scleralcyonacea. The genus Isis is an exception and is placed in Malacalcyonacea. Within Scleralcyonacea, most Calcaxonia members form one large, unnamed branch, while Ellisellidae and Dendrobrachiidae (and possibly Chelidonisididae) lie in other branches.

Calcaxonia originally included several families, and although some of these were updated in 2021, all of them were moved to the new order Scleralcyonacea in 2022.

In 2019, G. C. Williams proposed that the name Calcaxonia should apply to the whole clade now known as Scleralcyonacea—an idea that also includes Pennatulacea and Helioporacea. But not all researchers accepted this proposal.