Naviculoid diatoms (Bacillariophyta) of relict Lake Mogilnoye (Kildin Island, Barents Sea)

New data on morphology and taxonomy of 16 pennate diatom species of three orders Naviculales, Lyrellales and Thalassiophysales found in subpolar meromictic Lake Mogilnoye at salinity of up to 4 ‰ and water temperature of about 10 °С are presented. A new species, Navicula sepulchralis Gogorev et E. Lange, sp. nov., is described. Its valves are 38–46 μm long, 11–13 μm wide and have 9.5–10.5 striae per 10 μm and 23–24 areolae per 10 μm of striae. N. sepulchralis is very similar to N. kohlmaieri in size of valves and number of striae, but differs in valve outline. Hippodonta cf. naviculiformis, Pinnularia birnirkiana, Seminavis barbara and Staurophora anuschkae were recorded for the first time in Russia, as well as a taxon, Chamaepinnularia krookiformis, — for the first time in the Murmansk Region, nine species were detected for the first time in the lake.