Sea anemones (order Actiniaria) are among the most diverse and successful members of the anthozoan subclass Hexacorallia, occupying benthic marine habitats across all depths and latitudes. Actiniaria comprises approximately 1,200 species of solitary and skeleton-less polyps and lacks any anatomical synapomorphy. Although monophyly is anticipated based on higher-level molecular phylogenies of Cnidaria, to date, monophyly has not been explicitly tested and at least some hypotheses on the diversification of Hexacorallia have suggested that actiniarians are para- or poly-phyletic. Published phylogenies have demonstrated the inadequacy of existing morphological-based classifications within Actiniaria. Superfamilial groups and most families and genera that have been rigorously studied are not monophyletic, indicating conflict with the current hierarchical classification. We test the monophyly of Actiniaria using two nuclear and three mitochondrial genes with multiple analytical methods. These analyses are the first to include representatives of all three currently-recognized suborders within Actiniaria. We do not recover Actiniaria as a monophyletic clade: the deep-sea anemone Boloceroides daphneae, previously included within the infraorder Boloceroidaria, is resolved outside of Actiniaria in several of the analyses. We erect a new genus and family for B. daphneae, and rank this taxon incerti ordinis. Based on our comprehensive phylogeny, we propose a new formal higher-level classification for Actiniaria composed of only two suborders, Anenthemonae and Enthemonae. Suborder Anenthemonae includes actiniarians with a unique arrangement of mesenteries (members of Edwardsiidae and former suborder Endocoelantheae). Suborder Enthemonae includes actiniarians with the typical arrangement of mesenteries for actiniarians (members of former suborders Protantheae, Ptychodacteae, and Nynantheae and subgroups therein). We also erect subgroups within these two newly-erected suborders. Although some relationships among these newly-defined groups are still ambiguous, morphological and molecular results are consistent enough to proceed with a new higher-level classification and to discuss the putative functional and evolutionary significance of several morphological attributes within Actiniaria.

The combination of coloniality and symbiosis in Scleractinia is thought to confer competitive advantage over other benthic invertebrates, and it is likely the key factor for the dominance of corals in tropical reefs. However, the extant Scleractinia are evenly split between zooxanthellate and azooxanthellate species. Most azooxanthellate species are solitary and nearly absent from reefs, but have much wider geographic and bathymetric distributions than reef corals. Molecular phylogenetic analyses have repeatedly recovered clades formed by colonial/zooxanthellate and solitary/azooxanthellate taxa, suggesting that coloniality and symbiosis were repeatedly acquired and/or lost throughout the history of the Scleractinia. Using Bayesian ancestral state reconstruction, we found that symbiosis was lost at least three times and coloniality lost at least six times, and at least two instances in which both characters were lost. All of the azooxanthellate lineages originated from ancestors that were reconstructed as symbiotic, corroborating the onshore-offshore diversification trend recorded in marine taxa. Symbiotic sister taxa of two of these descendant lineages are extant in Caribbean reefs but disappeared from the Mediterranean before the end of the Miocene, whereas extant azooxanthellate lineages have trans-Atlantic distributions. Thus, the phyletic link between reef and nonreef communities may have played an important role in the dynamics of extinction and recovery that marks the evolutionary history of scleractinians, and some reef lineages may have escaped local extinction by diversifying into offshore environments. However, this macroevolutionary mechanism offers no hope of mitigating the effects of climate change on coral reefs in the next century.coral reefs | Bayes Traits | zooxanthellae | ancestral state reconstruction | phylogeny I n most marine organisms, coloniality is thought to have evolved from solitary ancestors and proceeded through progressive weakening of zooidal individuality in favor of increased individualization of the colony (1). In Scleractinia, colonial species are thought to have originated from solitary ancestors, most likely via incomplete asexual budding (2). This notion is almost intuitive, since all sexually produced coral colonies start as a larva that metamorphoses into a single polyp. Colonial integration supposedly increased in evolutionary time through dissolution of skeletal barriers among polyps (2-4). This range of morphological variability is in full display in extant Scleractinia, from the exclusively solitary species within the genus Anthemiphyllia, to the "quasicolonial" Anomocora carinata, in which "the daughter corallites [break] free of the parent before a third generation bud appears" (5), to the loosely integrated colonies of Rhizosmilia maculata in which partial colonial mortality may yield solitary daughter polyps and finally the highly integrated colonies of Favia favus, in which polyp damage invariably results in a colony-wide regenerative response (6). Although most...

Acontia-nematocyst-dense, thread-like extensions of the mesenterial filaments-are the characteristic feature of the actiniarian group Acontiaria. Phylogenetic analyses have shown that acontiate taxa form a clade that also includes some taxa without acontia. We analyse five molecular markers from 85 actiniarians to explore the phylogenetic relationships among families in Acontiaria, including acontiate species assigned to other higher taxa and species without acontia that have been allied to Acontiaria. Based on our results, we redefine the group to accommodate those lineages that have lost acontia, and formalize it as superfamily Metridioidea. Based on stable and well supported clades, we resurrect Phelliidae and Amphianthidae, redefine Kadosactinidae and Actinoscyphiidae, and move two species to new genera: that previously termed Sagartiogeton erythraios belongs in Jasonactis gen. nov.; and that previously termed Anthosactis pearseae belongs in Ostiactis gen. nov., type genus of Ostiactinidae fam. nov. We also synonymized Halcampoididae and Halcampidae (as Halcampidae) and Andvakiidae and Isophelliidae (as Andvakiidae). The results of our phylogenetic analyses indicate that the diagnostic morphological characters used in the family-level taxonomy of acontiate actiniarians such as the nematocysts of the acontia, the marginal sphincter muscle, and mesenteries divisible into macro-and microcnemes, have to be revisited, as these features are highly homoplasious.

Scleractinian corals, which include the architects of coral reefs, are found throughout the world's oceans and have left a rich fossil record over their 240 million year history. Their classification has been marked by confusion but recently developed molecular and morphological tools are now leading to a better understanding of the evolutionary history of this important group. Although morphological characters have been the basis of traditional classification in the group, they are relatively few in number. In addition, our current understanding of skeletal growth and homology is limited, and homoplasy is rampant, limiting the usefulness of morphological phylogenetics. Molecular phylogenetic hypotheses for the order, which have been primarily focused on reef-building corals, differ significantly from traditional classification. They suggest that the group is represented by two major lineages and do not support the monophyly of traditional suborders and most traditional families. It appears that once a substantial number of azooxanthellate taxa are included in molecular phylogenetic analyses, basal relationships within the group will be clearly defined. Understanding of relationships at lower taxonomic levels will be best clarified by combined analyses of morphological and molecular characters. Molecular phylogenies are being used to inform our understanding of the evolution of morphological characters in the Scleractinia. Better understanding of the evolution of these characters will help to integrate the systematics of fossil and extant taxa. We demonstrate how the combined use of morphological and molecular tools holds great promise for ending confusion in scleractinian systematics.