Taxonomical study of diatom Navicula hedinii in Vrana Lake, Croatia and its transfer to a new genus

The population of an unknown naviculoid diatom from karstic, polymictic Lake Vrana in Croatia was identified as Navicula hedinii Hustedt, a species that was described in 1922 from a small lake in eastern Turkestan. The occurrence of Navicula hedinii in samples collected for the study of the relationship between phytoplankton and environmental variables in a lake, allowed a detailed study of the morphological features of this diatom species using light microscopy (LM), scanning (SEM) and transmission electron microscopy (TEM). Type material collected by Sven Hedin and kept at the Friedrich Hustedt Diatom Collection in Bremerhaven was also examined using light and scanning electron microscopy. These results, the possible conspecificity with the Croatian species and the implication for the correct taxonomical position of this species are discussed. Based on the ultrastructure of this species, it can no longer be included within the taxonomical concept of Navicula s.s. Bory. Due to the large similarity species Navicula pseudocrassirostris Hustedt certainly stands very near to Navicula hedinii and it is used in the comparison. Following a comparative morphological analysis of species with genera bearing similar characters (Adlafia, Veigaludwigia, Kobayasiella, Cavinula, Stenoneis, Climaconeis, Berkeleya, Sellaphora, Cosmioneis), a new genus, Envekadea Van de Vijver, Gligora, Kralj & Cocquyt gen. nov. is proposed. The genus name Envekadea is derived from the NVKD (Nederlands-Vlaamse Kring van Diatomisten), the association of the Dutchspeaking diatomists. The name was chosen to underline its relationship with Adlafia, a genus named after the Association of the French-speaking diatomists (ADLaF)