<em>Fragilaria longwania</em> sp. nov. (Bacillariophyceae), a New Araphid Diatom from Sihailongwan Maar Lake, Northeastern China

A new species, Fragilaria longwania sp. nov., from Sihailongwan Maar Lake in northeastern China, is described on the basis of observations made using light microscopy (LM) and scanning electron microscopy (SEM) that reveal the distinctive features that separate this new taxon from the other species currently placed in the genus Fragilaria. Fragilaria longwania sp. nov. has relatively short valve length, high stria density, spindle-shaped valves with a swollen and sometimes deformed central area and capitate valve apices, short spines and weakly developed apical pore fields. This combination of character was found to be unique when the new species was compared with morphologically similar taxa. This species was found in various samples collected from Sihailongwan Maar Lake between 2003 and 2017. The analysis of the diatom assemblages collected in the sediment trap samples allowed an assessment of the cell size variation, seasonal occurrences and ecological requirements of this species. Fragilaria longwania appears to be a planktonic diatom associated with the spring season.