Molecular and morphological analysis of Biddulphia sensu lato: a new diagnosis of Biddulphia, with a description of the new genera Biddulphiella and Neobrightwellia

The diatom genus Biddulphia Gray has hosted a tremendous amount of morphological diversity throughout its taxonomic history. SEM-assisted studies have significantly helped to sort this diversity into a classification based on specific valve characters, particularly the structure of pore fields on the valve apices, rather than gross morphology such as valve outline. Recent molecular phylogenetic analyses, however, have suggested that even the revised diagnosis of Biddulphia has not led to a monophyletic genus. In this study, we have surveyed the morphology of both fossil and extant taxa and have found a significant disparity in the number of Biddulphia taxa featuring valves with deep folds—sulci—rather than internal crosswalls—costae. Based on these observations, we have proposed several taxonomic revisions around this character, including the creation of two new genera—Biddulphiella gen. nov. and Neobrightwellia gen. nov.—and the transfers of several fossil and extant biddulphioid taxa to genera (Donskinica Kozyrenko, Stoermeria Kociolek, L.Escobar & S.Richardson and Tabulina J. Brun) which are more appropriate to their morphology.