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 understanding phylogenetic relationships. The relationship among stony corals (order Scleractinia), sea anemones (order Actiniaria), and corallimorpharians (order Corallimorpharia) has been particularly problematic. We synthesize existing 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 traditional 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 about skeletal evolution and subordinal taxonomy remain unanswered pending denser taxonomic and character sampling. CC, Willis BL. 1986. Synchronous spawnings of 105 scleractinian coral species on the Great Barrier Reef. Marine Biology 90: 379-394. Bayer FM, Grasshoff M, Verseveldt J. 1983. Illustrated trilingual glossary of morphological and anatomical terms applied to Octocorallia. Leiden: EJ Brill. Berntson EA, France SC, Mullineaux LS. 1999. Phylogenetic relationships within the class Anthozoa (Phylum Cnidaria) based on nuclear 18S rDNA sequences. Molecular Phylogenetics and Evolution 13: 417-433. Brown WM, Pranger EM, Wang A, Wilson AC. 1982. Mitochondrial DNA sequences of primates: tempo and mode of evolution.

Ptychodactiaria, currently recognized as an order equivalent to Actiniaria (sea anemones sensu stricto) and Scleractinia (`true' or hard corals) of cnidarian class Anthozoa, contains three monotypic genera, Dactylanthus, Ptychodactis, and Preactis, in two families, Ptychodactiidae and Preactiidae. Features that had been considered distinctive to the order among hexacorallian anthozoans were that gametes mature in protrusions from the mesenteries, as in octocorallian anthozoans, and that gametes do not mature embedded in mesogloea. However, we found that ptychodactiarian gametes develop in the mesenteries, surrounded by mesogloea, as in other sea anemones. We conclude that the three species constitute a clade, the most distinctive feature of which is medially fused mesenteries at the proximal end of the body. This clade merits subordinal status within order Actiniaria. We rede¢ne Ptychodactiaria and its component taxa, moving Dactylanthus from family Ptychodactiidae to family Preactiidae.

No abstract

No abstract