Taxonomy of three new Neidium Pfitzer species of the Arapiuns and Tapajos Rivers Basin (Santarem, Para, Brazil)

During our investigations on the taxonomy of diatoms of clear water habitats in the western Para region, we found three interesting, previously undocumented Neidium species. This study was based on samples taken from different habitats (plankton and sediment) in the Arapiuns and Tapajos Rivers, as well as three lakes. Based on light and scanning electron microscope observations, three new Neidium are distinguished from one another and their congeners by differences in valve outline, stria density, striation pattern, number and position of longitudinal canals and external proximal raphe endings. Furthermore, we provide formal descriptions of these new species and compare them with others similar species. We also discuss variation in several features of taxa currently assigned to the genus Neidium.