Linking new DNA sequence data to old scientific names of <i>Parvodinium</i> (Peridiniopsidaceae, Dinophyceae)

<i>Parvodinium</i> (Peridiniopsidaceae) comprises a fairly species-rich group of relatively small peridinialean dinophytes that differ only in inconspicuous traits. No DNA sequence information is available for many of these species, although such links are important for their unambiguous identification. We examined two species of <i>Parvodinium</i> using light and scanning electron microscopy. Sequences of the rRNA complex (including 32 new GenBank entries) were obtained and embedded in a representative taxon sample of Peridiniopsidaceae for molecular phylogenetics. Based on DNA sequence comparison the two species are closely related and comprise the sister group to <i>Parvodinium marciniakii</i>. The morphologies grossly matched the descriptions of <i>Parvodinium dzieduszyckii</i> and <i>Parvodinium lubieniense</i>, respectively, to which the studied materials are tentatively assigned. Our approach of integrative taxonomy provides links between morphologies and DNA sequences, filling the gaps in reference data bases that are essential in metabarcoding studies. Species of <i>Parvodinium</i> are not identifiable based on a single autapomorphy but rather based on a unique combination of traits. Developmental processes of both species, such as vegetative mitosis and sexual reproduction, appear similar to other species of <i>Parvodinium</i>, but life history of dinophytes remains understudied in general. Distinct and unique combination of traits characterise species of <i>Parvodinium.</i>V4 SSU sequences diagnostic for species of <i>Parvodinium.</i>Vegetative cell division (eleutheroschisis) outside parental theca. Distinct and unique combination of traits characterise species of <i>Parvodinium.</i> V4 SSU sequences diagnostic for species of <i>Parvodinium.</i> Vegetative cell division (eleutheroschisis) outside parental theca.