Actinioidea, Rafinesque, 1815

Daly, M., Crowley, L. M., Larson, P., Rodríguez, E., Heestand Saucier, E. & Fautin, D. G., 2017, Anthopleura and the phylogeny of Actinioidea (Cnidaria: Anthozoa: Actiniaria), Organisms Diversity & Evolution (New York, N. Y.) 17 (3), pp. 545-564 : 556-557

Phylogeny of Actinioidea and Actiniidae

Our trees concur with most broad-scale analyses of Actiniaria (e.g., Daly et al. 2008; Rodríguez et al. 2012; but see Rodríguez et al. 2014) in finding a monophyletic Actinioidea . One notable difference is that E. lisbethae was not recovered within Actinioidea by Rodríguez et al. (2014); our denser sampling of Epiactis specifically and Actinioidea effectively resolves what Rodríguez et al. (2014) considered a spurious placement. Despite consistent and relatively strong support for ingroup monophyly, our analyses do not effectively resolve relationships among the major groups within Actinioidea . The internal branches at the deepest nodes are short, their resolution is not well supported, and the differences among the data sets largely reflect alternative interpretations of the basal branching order.

We find that Actiniidae is polyphyletic with respect to other families of Actinioidea : the node at which all taxa currently within Actiniidae are monophyletic is the node that includes all members of Actinioidea . Despite failing to recover a monophyletic Actiniidae , the combined, mitochondrial, and nuclear trees agree on many clades and recover several groups consistently or with high support, and thus provide a starting point for circumscribing groups within Actinioidea . Our taxon sampling precludes taxonomic revision for most groups because of its incompleteness at the genus- and family-level and because almost all of the clades we identify include members of multiple genera, if not multiple families. Furthermore, at present, none of these groups are clearly definable based on features typically used for classification. Defining the boundaries and membership of these and identifying the features by which these can be recognized is beyond the scope of the present study, but will be facilitated by the delimitation of these broad groupings.

The combined tree and the single-data set analyses differ in their interpretation of the primary split within Actinioidea . In both the mitochondrial and nuclear trees, species that are part of the EA and L clades form a grade sister to the majority of ingroup species (Supplemental Figs. 1 and 2 ), whereas the combined data tree recovers the EA and L as sister clades within the large ingroup clade ( Fig. 2 ). Although Larson and Daly (2016) studied relatively fewer lineages in Actiniidae , their analyses included relatively denser sampling of what here constitutes the EA group, and they found support for EA and L as a grade outside of a clade that included species of e.g., Actinia , Anthopleura , Bunodactis , Bunodosoma , Gyractis , and Oulactis . The ecology, bathymetric distribution, and natural history of species in the EA and L groups are more varied than that of the species in the rest of the ingroup. The different interpretations of the relative position of the taxa in the EA and L groups are important for interpreting the evolution of features like acrorhagi (discussed below) and for understanding the evolution of photosymbiosis or asexual reproduction. Especially in light of their diversity in biology, the EA and L lineages are probably under sampled relative to the rest of the ingroup in our analyses, but this is necessary, given our primary interest in Anthopleura and its monophyly. We anticipate that denser sampling of the groups represented in the EA and L clades will resolve this instability.

All of our analyses find a sister-group relationship between the ptychodactiarians and the South African species K. natalensis and A. stephensoni . In their description of Korsaranthus, Riemann-Zürneck and Griffiths (1999) note the similarity of K. natalensis to Dactylanthus and other ptychodactiarians with respect to the anatomy of the actinopharynx and cnidom. However, they interpret these as convergent similarities based on similar diet and mode of locomotion, an interpretation accepted by Cappola and Fautin (2000). Although several attributes that have been interpreted to support their separation as a higher taxon (reviewed by Cappola and Fautin 2000), the affiliation between ptychodactiarians and actiniids has been recovered in several molecular phylogenetic analyses ( Daly et al. 2003, 2008; Rodríguez et al. 2012, 2014) and the sister group relationship between the clade containing the ptychodactiarians Dactylanthus and Preactis and members of the B clade is consistent across data sets.

Our results have clear implications for a handful of relatively minor taxonomic issues. We never find monophyly of the included species of Anemonia , Aulactinia , Epiactis , or Urticina ( Fig. 2 ). Members of Bunodosoma are divided between the B and A clades within the ABEPP clade in groupings that are both consistent across analyses and well supported in the combined analysis. The placement of A. biscayensis outside of Bunodosoma (and sister to other nominal Anthopleura ) supports the reassignment of this species proposed by Daly (2004b). A. viridis and A. ballii are recovered as sister taxa in all analyses. Although assigned to different genera and distinct in the anatomy of the column (smooth in A. viridis , verrucose in A. ballii ), these northern hemisphere species are similar in having weakly muscled columns and nonretractile tentacles and are also similar in coloration (see Stephenson 1935). The other species of Anemonia includ- ed in this analysis, A. erythraea and A. natalensis , are southern hemisphere species that group with P. varia in the highly supported SA clade. The close association we find between Aulactinia and the Northern hemisphere species of Epiactis was also found in a more narrowly focused analysis ( Larson and Daly 2016) but is not obvious in terms of anatomy: the included species of Aulactinia have a verrucose column whereas that of Epiactis is smooth ( Tables 2 and 3). All of these polyphyletic genera ( Anemonia , Aulactinia , Bunodosoma , Epiactis , Urticina ) require revision. In addition, we find that Actinia , Isosicyonis , and Liponema are paraphyletic, but acknowledge that support for their paraphyly is weak and these lineages have not been the focus of our sampling.

Dunn et al. (1980) conditionally proposed a synonymy between Bunodactis and Aulactinia . Although this proposal was limited in the scope of the synonymy and advocated further study, it has been generally adopted (without the recommended specimen-level studies), and most authors now apply Aulactinia as the valid name for the species originally described as Actinia verrucosa (see Fautin 2016), although this is not uniformly the case ( Spano et al. 2013, Garese et al. 2014). Because we never find a close relationship between B. verrucosa and species of Aulactinia , we reject the proposition that Bunodactis is wholly in synonymy with Aulactinia and

Figures

Fig. 2 Maximum likelihood tree resulting from analysis of combined data set. Branch lengths are to scale. Bootstrap values (1000 replicates) greater than 75% are indicated. Clade labels apply to taxa within each shaded box