This electron microscopy study of materials from waterbodies and watercourses in the far north of Western Siberia (Gudan, Taz and Yamal peninsulas), Eastern Siberia (Cis-Baikal, Yakutia) and Northwest Russia made it possible to obtain new data on the morphology of a number of representatives of the genus Hippodonta Lange-Bertalot, Metzeltin et Witkowski (H. capitata (Ehrenberg) Lange-Bertalot, Metzeltin et Witkowski, H. coxiae Lange-Bertalot, H. costulata (Grunow), Lange-Bertalot, Metzeltin et Witkowski, H. hungarica (Grunow), Lange-Bertalot, Metzeltin et Witkowski, H. linearis (Østrup) Lange-Bertalot, Metzeltin et Witkowski, H. pseudopinnularia Lange-Bertalot, H. pumila Lange-Bertalot, H. subcostulata (Hustedt) Lange-Bertalot, Metzeltin et Witkowski), specifying the systematic positions of some forms and ranges of species under study. The following new for science species have been described: H. yunetayakhiensis Genkal et Yarushina sp. nov., H. nikolaevii Genkal et Yarushina sp. nov., H. moiseevae Genkal et Yarushina sp. nov., H. yunetayakhiensis is similar to H. naviculiformis A. Pavlov, Z.Levkov, D.M. Williams et Edlund, and H. lange-bertalotii Van de Vijver, Mataloni et Vinocur but differ from them in quantitative characteristics (valve length and width, number of striae in 10 µm). By the presence of fascia in the central area, H. nikolaevii is similar to H. latelanceolata A.Pavlov, Z.Levkov, D.M.Williams et Edlund, H. costulatiformis Lange-Bertalot, Metzeltin et Witlowski var. costulatiformis, H. costulatiformis var. densistriata A.Pavlov, Z.Levkov, D.M.Williams et Edlund, H. abunda A.Pavlov, Z.Levkov, D.M.Williams et Edlund, H. media A.Pavlov, Z.Levkov, D.M.Williams et Edlund, H. radiata A.Pavlov, Z.Levkov, D.M.Williams et Edlund, H. angustata A.Pavlov, Z.Levkov, D.M.Williams et Edlund, and H. microcostulata Metzeltin, Kulikovskiy et Lange-Bertalot) but the new species differ from the ones listed above by some quantitative characteristics and the shape of valve apices. Hippodonta moiseevae is similar to H. capitata but differs from the latter in quantitative characteristics. The list of representatives of the genus Hippodonta in Russia has been increased from 27 to 31.
Keywords: Bacillariophyta, Hippodonta, electron microscopy, new species
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