Rhodomonas storeatuloformis sp. nov. (Cryptophyceae, Pyrenomonadaceae), a new cryptomonad from the Black Sea: morphology versus molecular phylogeny

We established a new cryptomonad species, Rhodomonas storeatuloformis sp. nov., based on morphological and molecular characters of cultured strain isolated from the Black Sea. Cells are slightly dorsoventrally flattened, obloid in shape, 12-19 tim in length and 5-10 tim in width, with light-brown, parietal H-shaped chloroplast and a central pyrenoid. Two unequal flagella are located subapically in a short V-shaped vestibulum with a ligule on the left side. Cells are covered by a sheet-like papillate perisplast with numerous small underlain ejectosomes; discharged ejectosomes form distinctly visible minute pores. Mid-ventral band is absent. In general, cell morphology is very similar to described strains of Storeatula genus. However, phylogenetic analyses based on sequences of the partial nuclear 18S, 28S rDNA, and complete internal transcribed spacer (ITS) region of rDNA placed the novel cryptomonad strain within Rhodomonas genus as a separate clade. The predicted secondary structure of nuclear rDNA ITS2 has numerous compensatory base changes compared to the closest relative strains that support the distinction of the novel species among Rhodomonas taxa. The present results contribute to the study on still hidden cryptomonad biodiversity in the Black Sea. Contradiction between morphology and phylogenetic data in R. storeatuloformis further argues for revision of the generic delineations in the family Pyrenomonadaceae.