Molecular and morphological systematics of the Ellisellidae (Coelenterata: Octocorallia): Parallel evolution in a globally distributed family of octocorals

•Ellisellidae requires at least six new genera plus revision of current genera.•Biogeography important systematic character in addition to morphology.•Sea fan is the ancestral state for Ellisellidae.•Directional and parallel diversification into similar growth forms.•Convergence of forms suggests genetic constraint on morphological limits.

The octocorals of the Ellisellidae constitute a diverse and widely distributed family with subdivisions into genera based on colonial growth forms. Branching patterns are repeated in several genera and congeners often display region-specific variations in a given growth form. We examined the systematic patterns of ellisellid genera and the evolution of branching form diversity using molecular phylogenetic and ancestral morphological reconstructions. Six of eight included genera were found to be polyphyletic due to biogeographical incompatibility with current taxonomic assignments and the creation of at least six new genera plus several reassignments among existing genera is necessary. Phylogenetic patterns of diversification of colony branching morphology displayed a similar transformation order in each of the two primary ellisellid clades, with a sea fan form estimated as the most-probable common ancestor with likely origins in the Indo-Pacific region. The observed parallelism in evolution indicates the existence of a constraint on the genetic elements determining ellisellid colonial morphology. However, the lack of correspondence between levels of genetic divergence and morphological diversity among genera suggests that future octocoral studies should focus on the role of changes in gene regulation in the evolution of branching patterns.

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