Re-evaluation of Amphidiniopsis (Dinophyceae) Morphogroups Based On Phylogenetic Relationships, and Description of Three New Sand-dwelling Species From the NW Mediterranean

Amphidiniopsis is a diverse genus of thecate heterotrophic dinoflagellates within the benthic, sand-dwelling species, with more than 20 currently described. Although molecular information about members of this genus is still scarce, morphological heterogeneity suggests the genus is paraphyletic. We investigated the diversity of Amphidiniopsis species in the NW Mediterranean Sea by morphological and molecular approaches, which led to the description of three new species, A. bulla sp. nov., A. erinacea sp. nov., and A. selene sp. nov. Phylogenetic reconstructions based on SSU and LSU rDNA sequences obtained from individual cells and the observed morphological characters confirm, as previously suggested, the paraphyly of the genus and the existence of at least four phylogenetic subgroups, instead of the three main subgroups defined to date. We also morphologically characterized Herdmania litoralis, suggesting the existence of more than one species belonging to this monotypic genus. Herdmania is a sister taxon to Amphidiniopsis, both morphologically and phylogenetically, and given the paraphyly of the latter, it should be considered a member of the newly termed Amphidiniopsis genus complex. The finding of the three new species highlights that the Mediterranean harbors distinctive, sand-dwelling dinoflagellates and needs further investigations of its unexplored diversity.