Original Article SYSTEMATICS OF THE HEXACORALLIAM. DALY ET AL.

The composition of and relationships among higher-level groups within the anthozoan subclass Hexacorallia Zoantharia) has been controversial because independent analyses of anatomy, life history, ultrastructure, and molecular sequences have failed to provide a consistent framework for drawing taxonomic boundaries or under-standing phylogenetic relationships. The relationship among stony corals (order Scleractinia), sea anemones (order Actiniaria), and corallimorpharians (order Corallimorpharia) has been particularly problematic. We synthesize exist-ing studies and provide new anatomical and molecular evidence that bear on the question of ordinal circumscription and relationships. We find that orders Actiniaria, Antipatharia, Ceriantharia, Corallimorpharia, Scleractinia, and Zoanthidea are monophyletic; Corallimorpharia is most closely related to Scleractinia. We infer that many tradi-tional diagnostic characters are shared primitive features and thus poor indicators of phylogenetic relationships. Although the major nodes of the hexacorallian tree are well supported by multiple types of data, questions abou