Four new species of the genus Lacustriella (Bacillariophyta) from Lake Baikal

: We add four new species to the recently established genus Lacustriella Kulikovskiy, Lange–Bertalot et Metzeltin and characterize morphology of the taxa based on LM and SEM observations. Lacustriella cuspidata , L. rombea , L. radiata and L. solita share all of the typical morphological features of the genus including longitudinal canal along each valve margin, radiate uniseriate striae terminated with large elongated areolae, and external distant raphe ends bent oppositely. L. cuspidata is peculiar among the other Lacustriella with rows of small pores look as if they continue striae on the surface of longitudinal canals as well as with the axial area sharply widened into the asymmetrical central area. L. rombea is different in combination of valve outline with unprotracted rostrate apices, irregular areolation at centre of the external valve, and slit–like areola occluded with volae. In L. radiata distinctive characters include protracted rostrate valve apices, rhombic central area and volated slit–like areolae. L. solita differs in the highest density of areolae in striae and an ornamented surface of longitudinal canals. New species were compared to the closest morphologically similar taxa. Some general ecological properties and distribution in the littoral zone of the ancient lake are given. microscope (Zeiss, Gottingen, Germany) with a 100× oil immersion objective. LM photographs were taken with an attached TOUPCAM TM DC UA1000CA camera. For scanning electron microscopy 50 µl aliquot of the suspension of cleaned valves was placed on aluminium stub, dried on air, coated with a gold in Balzers SCD 004 sputter coater and examined with an FEI Quanta 200 scanning electron microscope (Eindhoven, Netherland) at a working distance of 10 mm and acceleration voltages of 25–30 kV. Measurements of valves, density of striae and areolae in striae were taken for each photographed cell; at least 20 individuals of each taxon were studied. Valve structure terminology follows K rammer & L ange –B ertalot (1986), R ound et al. (1990) and K ulikovskiy et al. (2012, 2016).