Phylogenetic relationships among scleractinians, actiniarians, and corallimorpharians (Coelenterata: Anthozoa)

Abstract

Using radioimmunoassay, with Ceriantharia as the outgroup, we tested whether corallimorpharians are so closely related to scleractinians that they should be considered members of that order. From analysis of distance data, we infer that the two lineages of corallimorpharians (tropical, plate-like zooxanthellate forms and largely temperate/deep sea, columnar, azooxanthellate ones) are as closely related to a lineage of deep-sea corals as they are to one another. We therefore concur with the minority opinion that Corallimorpharia does not constitute an order distinct from and equivalent in rank to Scleractinia. We further infer that Actiniaria, which branches from a different lineage of Scleractinia, may not represent a separate order, either. These data support morphological evidence that scleractinians are ancestral to corallimorpharians and actinians, contrary to the general paradigm. We speculate that both corallimorpharians and actinians may have had multiple origins from corals, and that other groups of non-skeletalized polyps, now extinct, may also have arisen from corals.