Fallacia tenera

Valves are linear-elliptic to elliptic. The axial area is straight, narrow and contains a filiform, straight raphe. A narrow, lanceolate lyre-shaped hyaline area is present on either side of the axial area. The striae are radiate to nearly parallel and composed of distinct areolae. Striae are interreupted longitudinally by a hyaline rib, which divides the striae into two areolae. The areolae closer to the mantle are larger, one per stria, and uniform in shape and size. The inner areolae are smaller, one per stria, and uniform in shape and size. The central area is small. Areolae adjacent to the raphe branches form a single row on one side, but sometimes there are a few areolae or an incomplete row of areolae on the other side of the raphe.

The presented concept of F. tenera is strictly based on observations of the type material of Navicula tenera Hustedt from Ranu Klindungan Lake in Java and corresponding morphologies observed in streams in California. This concept is in accordance with Patrick and Reimer (1966). More recent taxonomic treatments, such as Krammer and Lange-Bertalot (1986) and Cantonati et al. (2017) are broader, including several taxa, originally described as separate species (for discussion see Li et al., 2014, Stancheva and Manoylov 2017).