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

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 tre es derived from the morphological data did not coincide closely with the mo lecular data, and the presence of several polytomies at some nodes of the t rees resulted in ambiguities among the systematic relationships. On the oth er hand, the combined analysis using total evidence presents a more resolve d and highly supported topology, as is indicated by higher bootstrap values and decay indices than either analysis alone. However, strict and semi-str ict consensus trees derived from taxonomic congruence show a poorer resolut ion for the phylogeny of Anthozoa. The trees constructed from the molecular data, using neighbor-joining and maximum-likelihood methods, are nearly co ngruent with the result from the total evidence. Based on these results, An thozoa is divided into three subclasses: Alcyonaria, Zoantharia, and Cerian tipatharia. 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 Penn atulacea is basal, and orders Alcyonacea and Telestacea branch later. The o rder Gorgonacea is divided into two suborders, Holaxonia and Scleraxonia. B ellonela is more related to order Stolonifera, forming a monophyletic group . In Zoantharia, the order Zoanthinaria is basal, and the remaining taxa ar e divided into two clades: one includes the order Actiniaria and the other includes orders Antipatharia, Corallimorpharia, and Scleractinia. The latte r two orders form a monophyletic group. This study presents a different phy logeny of actiniarians from the earlier hypothesis of scleractinian ancestr y.