Placoneis explanata

Valves are linear-lanceolate, with weakly convex margins. Apices are rostrate and bluntly rounded. The axial area is linear and narrow. The central area is variable, from bow-tie to rectangular in shape. The raphe is straight and weakly lateral. The proximal raphe ends are weakly inflated. The distal raphe ends are deflected to opposite sides of one another. Striae are radiate and weakly curved at the center of the valve, becoming straight, parallel and finally, more dense at the apices. The striae on the primary side occur 11-12 in 10 µm and on the secondary side, 10-11 in 10 µm. The areolae are round to slightly apically elongate and occur 24-26 in 10 µm.

This taxon was originally described as Navicula explanata Hustedt (1948) and later transferred to Placoneis explanata (Hustedt) Mayama in Mayama and Kawashima (1998). Lange-Bertalot published a later homonym (Placoneis explanata (Hustedt) Lange-Bertalot in Rumrich et al. 2000 nom. illegit). The earlier name, P. explanata (Hustedt) Mayama in Mayama and Kawashima has priority.