Cymbella affinis

Valves are strongly dorsi-ventral, with subrostrate to rostrate apices. The dorsal margin is strongly arched, whereas the ventral margin is slightly convex or flat, often excised. The axial area is narrow, linear. The central area is very small or not distinct. One stigma is present at the end of the middle striae. The proximal raphe ends have central pores that curve to the ventral side. The raphe is lateral, becoming filiform near the distal end. Striae are slightly radiate. The areolae number 25-30 in 10 μm.

Note that this concept of Cymbella affinis is based on Kützing's type material examined by Reimer (see image below) and by Tuji (2007) and is different from the concept of Krammer (2002). Krammer examined material labeled C. affinis in W. Smith's collection within the Van Heurck collection, Antwerp, which contains C. tumidula Grunow. Therefore, Krammer claimed that these two species are synonymous and the name C. affinis has to be applied to diatom so far known as C. tumidula. Reimer's (below) and Tuji (2007) photographs of the type material of C. affinis, show, however, that Krammer's decision is incorrect, while C. affinis and C. excisa are conspecific. Kützing applied the name C. affinis to specimens without excision and C. excisa to specimens with excised ventral margin.