Search

Cyclotella lacuskarluki Manguin ex Kociolek & Reviers is a small diatom known only from the original drawing that provides little information on the morphology of this taxon. As Manguin's original materials are lost, recently collected samples from Lake Karluk, Alaska, the type locality of the species, were studied with light and scanning electron microscopy to determine its identity. As a result of this investigation, C. lacuskarluki is transferred here to the genus Discostella. Discostella lacuskarluki is 2.5–7 µm in diameter, has a shallow mantle, a stellar pattern of alveoli in the valve centre that may be reduced or completely absent, bifurcating costae and 4–5 marginal fultoportulae opening externally by short thickened tubes with round openings. We observed this species in numerous lakes across Alaska, in Lake Tahoe, Nevada, in several lakes across Canada, and in tundra and tree-line lakes of Northeastern Siberia. Although direct comparison with other Discostella species is difficult because the small size of these diatoms requires high-resolution imagery to reveal ultrastructural details, it appears that D. lacuskarluki is conspecific with D. tatrica Procházková et al. recently described from lakes of Central Europe and also reported from the European part of Russia. It is also conspecific with D. nipponica (Skvotzov) Tuji & D. M. Williams known from Japan. The apparent wide distributional range of this species indicates that it has been overlooked and commonly reported as D. pseudostelligera or D. stelligera in arctic, boreal and alpine lakes. [ABSTRACT FROM AUTHOR]

The genus Krsticiella Levkov was previously known only from the basins of Lakes Ohrid and Prespa, and from Lake Baikal. Examination of type materials of diatoms originally described by Niels Foged from the North Slope of Alaska revealed that Navicula lenis Foged and N. meadeensis Foged belong to Krsticiella, to which they are formally transferred here. One of these species, K. lenis, is also found in thermokarst tundra lakes of the Kolyma Lowland in Northeastern Siberia. Several illustrations in previously published floras of Pliocene and Pleistocene diatoms of Eurasia indicate wider past distributions of Krsticiella species. The current restriction of this genus to non-glaciated regions of the Arctic and large ancient lakes in temperate zone indicates that it is a Cenozoic relict. [ABSTRACT FROM AUTHOR]

Three rare Psammothidium species were found in recently surveyed lakes of Northeastern Siberia, Russia. One of these species found in lakes of the Kolyma Lowland, is new for science and is formally described here as Psammothidium onufrii sp. nov. It is morphologically similar to the brackish–water species Achnanthes punctulata, but it lacks a central area on rapheless valve and possesses a large central area on the raphe valve. Psammothidium onufrii is characteristic for tundra thermokarst lakes with moderate mineral content. Psammothidium sacculum previously reported from a few subarctic and arctic locations was found in several lakes of the Kolyma Lowland and of the Magadan District. The frustule ultrastructure of this species is documented for the first time here. The third species, known as Achnanthes obliqua (W. Gregory) Hustedt and transferred here to Psammothidium, is a morphologically distinct and relatively rare diatom occasionally reported from northern regions of Eurasia and Western North America. In Northeastern Siberia it was found in sediments of relatively large shallow lakes with low to moderate mineral content. Detailed morphological characterization of the three Psammothidium species will facilitate their detection in environmental surveys and their use in paleoenvironmental reconstructions. [ABSTRACT FROM AUTHOR]