Molecular Phylogeny of the Genus Cymbosellaphora (Bacillariophyceae, Cymbellales): Evolutionary Significance of Areolae Morphology vs. Structure of Pore Occlusions

This is an investigation of molecular phylogeny and morphology of the genus Cymbosellaphora (Bacillariophyceae, Cymbellales). For this study, a strain of Cymbosellaphora geisslerae isolated from the Plotnikova River (Kamchatka Territory, Russia) was studied using light, scanning, and transmission electron microscopy, as well as molecular methods. Phylogenetic analysis based on 18S rDNA and rbcL gene sequences revealed that Cymbosellaphora geisslerae belongs to the order Cymbellales and forms an alliance with representatives of genera Gomphonella and Reimeria. The results of molecular study are supported by morphology. In the course of molecular analysis, we discuss the diversity of valve morphology across Cymbosellaphora, Gomphonella, Reimeria and related genera. As a result, a new type of pore occlusions, typical for Cymbosellaphora, is proposed, the diagnoses of the genus Cymbosellaphora and the species Cymbosellaphora geisslerae are emended, and the epitypification of this species is made. Most importantly, our data indicates that the concepts of areolae morphology and pore occlusions structure in the order Cymbellales might require critical evaluation.