Molecular phylogeny of ocelloid-bearing dinoflagellates (Warnowiaceae) as inferred from SSU and LSU rDNA sequences

Molecular phylogenetic analyses of SSU and LSU rDNA sequences demonstrated that warnowiids form a well-supported clade that falls within the more inclusive Gymnodinium sensu stricto clade. These data also confirmed that polykrikoids are members of the Gymnodinium sensu stricto clade as well; however, a specific sister relationship between the warnowiid clade and the polykrikoid clade was unresolved in all of our analyses. Nonetheless, the new DNA sequences from different isolates of warnowiids provided organismal anchors for several previously unidentified sequences derived from environmental DNA surveys of marine biodiversity.Comparative morphological data and molecular phylogenetic data demonstrate that the polykrikoid and the warnowiid clade are closely related to each other, but the precise branching order within the Gymnodinium sensu stricto clade remains unresolved. We regard the ocelloid as the best synapomorphy for warnowiids and infer that the most recent common ancestor of polykrikoids and warnowiids possessed both nematocysts and photosynthetic plastids that were subsequently lost during the early evolution of warnowiids. Our summary of species and genus concepts in warnowiids demonstrate that the systematics of this poorly understood group is highly problematic and a comprehensive revision is needed.Dinoflagellates represent a major lineage of unicellular eukaryotes with unparalleled diversity and complexity in morphological features, molecular processes, nutritional modes and symbioses with distantly related organisms [1-3]. The ecological importance of dinoflagellates is also extraordinary; members of the group play key roles as marine primary producers, coral reef zooxanthellae, and (micro)consumers in aquatic communities around the globe. The monophyly of dinoflagellates and their relationship to other alveolate taxa – particularly apicomplexans and ciliates – have been convincingly demonstrated with congruent molecular phylogenetic data [e.g., [1,4-