A phylogenetic study of the Anthozoa (phylum Cnidaria) based on morphological and molecular characters

Abstract.

The phylogenetic relationships within the Anthozoa were re-evaluated based on 41 morphological characters and nuclear sequences of 18S ribosomal DNA (29 anthozoans as ingroups and 3 hydrozoans as outgroups). The parsimony trees derived from the morphological data did not coincide closely with the molecular data, and the presence of several polytomies at some nodes of the trees resulted in ambiguities among the systematic relationships. On the other hand, the combined analysis using total evidence presents a more resolved and highly supported topology, as is indicated by higher bootstrap values and decay indices than either analysis alone. However, strict and semi-strict consensus trees derived from taxonomic congruence show a poorer resolution for the phylogeny of Anthozoa. The trees constructed from the molecular data, using neighbor-joining and maximum-likelihood methods, are nearly congruent with the result from the total evidence. Based on these results, Anthozoa is divided into three subclasses: Alcyonaria, Zoantharia, and Ceriantipatharia. The Ceriantipatharia now includes only one order, Ceriantharia, since the order Antipatharia is more closely related to orders within the Zoantharia. The Alcyonaria is a monophyletic group, in which the order Pennatulacea is basal, and orders Alcyonacea and Telestacea branch later. The order Gorgonacea is divided into two suborders, Holaxonia and Scleraxonia. Bellonela is more related to order Stolonifera, forming a monophyletic group. In Zoantharia, the order Zoanthinaria is basal, and the remaining taxa are divided into two clades: one includes the order Actiniaria and the other includes orders Antipatharia, Corallimorpharia, and Scleractinia. The latter two orders form a monophyletic group. This study presents a different phylogeny of actiniarians from the earlier hypothesis of scleractinian ancestry.