New for the region and rare representatives of the genus Sellaphora D.G. Mann are recorded during this electron microscopy study in the phytoplankton of waterbodies and watercourses in the Far North of Western Siberia (Yamal, Tazovsky and Gydan peninsulas): S. difficillima (Hustedt) C.E. Wetzel, L. Ector & D.G. Mann, S. disjuncta (Hustedt) D.G. Mann and S. stauroneioides (Lange-Bertalot) Lange-Bertalot, Kulikovskiy et Witkowski emend. Genkal et Yarushina. This makes it possible to specify the ranges of these species and obtain new data on the frustule morphology of these taxa. The species S. difficillima is found in waterbodies and watercourses of the Tazovsky Peninsula (the Sobetyakha River, a nameless stream), S. disjuncta is recorded from the Yamal Peninsula (the Mordyyakha River basin – Lake Pebtavyto, Lake Pervoe, a nameless channel), and S. stauroneioides is the most widespread (Yamal, Tazovsky and Gydan peninsulas). Since these species are rare, there was little data on their morphology insufficient for accurate identification of these taxa. This scanning electron microscopy study makes it possible to obtain first internal valve views of S. difficillima, S. disjuncta and S. stauroneioides and the raphe structure as well as first data on the number of areolae in 10 µm of a stria in S. disjuncta and S. stauroneioides. It is shown that the ranges of variation in quantitative diagnostic characteristics (valve length and width, number of striae and areolae in 10 µm) in the species under study differ from the first description and published data, which indicates their higher morphological variability. The data obtained on the internal and external valve morphology as well as on the diagnostic quantitative characteristics makes it possible to refine the diagnosis of these taxa and refer S. pseudonana to the synonymy of S. stauroneioides.
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