Molecular phylogeny, morphology and distribution of Amphitetras antediluviana Ehrenberg from the Black Sea and the Sea of Azov

The intriguing large-celled species of Amphitetras antediluviana Ehrenberg was originally described as a fossil species (Ehrenberg, 1840), but later noted in a living state in various regions of the World ocean. Our recent studies revealed that the species has been found for the last decade in significant numbers in many habitats along the coast of the Azov-Black Sea basin. Two strains—the large valves from Laspi Bay, the Black Sea (BL-5_12092019) and the small valves from the Sea of Azov (AZ-12_24122019)—were isolated and analyzed using light and scanning electron microscopy along with molecular-genetic investigation. Specimens of the two populations differ in valve sizes and structure, however, their belonging to the same species was confirmed with the help of molecular analysis. Taxonomic positions of the strains of A. antediluviana isolated from two marine waterbodies were clarified. In addition, we provided a detailed morphological diagnosis of the species with a description of the valve ultrastructure and its elements, as well as geographical distribution and taxonomic history.