The genus Navicula in ancient basins. I. Two novelties from the Black Sea

Backgrounds and aims – In this paper results on Navicula s. str. species from the (sub)littoral zone of the Black Sea are presented. Navicula pinnata var. pontica Mereschk. was originally described from the Black Sea in the early 20th century but, due to mistakes, incorrectly referred to in the literature as Navicula pennata A.W.F.Schmidt var. pontica Mereschk. A second species, Navicula parapontica sp. nov. is described as new for science. Analysis of recent and historical diatom assemblages revealed that Mereschkowsky's taxon occurs abundantly. Nevertheless, it was subject of numerous misidentifications in the past; the same applies for the second species. The aim of our study was to clarify the identity and taxonomic position of these taxa. Methods – This study is based on both historical and recent samples. Recent sampling was performed along the Ukrainian (Crimea) coast. In addition, samples from the Black Sea, originally collected and studied by Proshkina-Lavrenko in 1948–1951 and only recently rediscovered, have been analyzed. Results are based on light and scanning electron microscopy examination. We compared line drawings of Mereschkowsky's taxon with illustrations of similar taxa focusing especially on Navicula pinnata Pant. and N. pennata A.W.F.Schmidt. Key results – Comparison of line drawings of Mereschkowsky's taxon revealed no resemblance to N. pinnata. Micrographs of N. pennata illustrated in our paper indicated that any infraspecific relationship between Mereschkowsky's taxon and N. pennata is unlikely. Hence, we propose a new name, Navicula pontica stat. nov. for Mereshkowsky's taxon. In historical samples N. pontica was accompanied by a similar, however, sufficiently different, species, described as new for science: Navicula parapontica sp. nov. Conclusion – Our study resulted in a status change of a taxon originally described as Navicula pinnata var. pontica. In addition N. parapontica was described as new for science. These results will facilitate future identification of both abundant Black Sea littoral diatoms