Nupela matrioschka sp. nov., Nupela thurstonensis comb. nov. and Nupela neogracillima comb. and nom. nov., (Bacillariophyceae): critical analysis of their morphology

Light and electron microscopic observations of the diatom flora from the Polistovo-Lovatsky Sphagnum bogs (Russia, Novgorod region) revealed the occurrence of an unknown species comparable to Navicula thurstonensis Kaczmarska, a taxon described from Hawaii. Nupela matrioschka is described here as a species new to science, based on its valve morphology typical for the genus Nupela Vyverman & Compere. The major features conforming to Nupela are the ultrastructure of the raphe system and areolae. We propose formal transfer of Navicula thurstonensis to Nupela as N. thurstonensis (Kaczmarska) Kulikovskiy, Lange-Bertalot & Witkowski comb. nov. Both species are compared to similar taxa belonging to Nupela described from temperate climate zones. Also proposed is transfer of Achnanthes gracillima Hustedt to Nupela. Since the epithet gracillima is not available due to the priority of Nupela gracillima (Hustedt) Lange-Bertalot 1993, we propose as a necessary new name Nupela neogracillima (Hustedt) Kulikowskiy & Lange-Bertalot comb. nov., nom. Nov.