Molecular phylogeny of the dinoflagellates Podolampas and Blepharocysta (Peridiniales, Dinophyceae)

In contrast to the typical peridinioid dinoflagellates, the podolampadaceans are characterised by the absence of both a cingulum and a depressed sulcus. Until now, gene sequences for typical core podolampadaceans were not available. Despite this, two genera that appeared related in small subunit rRNA gene (SSU rDNA) trees, the sand-dwelling Roscoffia and Lessardia, which was previously considered an unarmoured taxon, were ascribed to this group since they showed coincidences in the plate formula with the podolampadaceans. However, the classification of Lessardia and Roscoffia as podolampadaceans remains controversial. To test whether these two genera are actually podolampadaceans, we obtained the first SSU rDNA sequences of four species of Podolampas (the type P. bipes, and P. elegans, P. palmipes and P. spinifera) and a Blepharocysta species, morphologically similar to the type B. splendor-maris, from the type locality, western Mediterranean Sea. SSU rDNA phylogenies showed that podolampadaceans and Roscoffia formed a well-supported monophyletic group composed of two subclades: one for Roscoffia and Blepharocysta and one other for Podolampas species. The whole podolampadacean clade branched in the lineage comprising Gymnodiniales, Peridiniales and Prorocentrales. By applying different methods and taxon sampling, we obtained alternative obtained alternative branching topologies. Either the podolampadaceans branched with low statistical support with Heterocapsa, Scrippsiella and Peridinium, while Lessardia branched relatively far with other peridinioids, or Lessardia branched as sister clade of the podolampadaceans with moderate support. The position of Lessardia appeared to be very instable, largely depending on the taxonomic sampling used. Although members of the Diplopsalis group have been suggested as ancestors of the podolampadaceans, our SSU rDNA phylogenies did not support a close relationship between both clades.