Cleve to be a distinct taxon. From this position they construct an argument fo Gomphonema tumens Kociolek and Stoermer to be distinct and that Gomphonema vibrio is not the initial vlave of G. tumens as could be suggested. In the tumid stage, G. vibrio is larger than G. tumens. As G. vibrio decreases in size the outline becomes more straight sided, tapering from the center to the headpole and footpole. Gomphonema tumens retains some of the tumid center even in the smaller valves.
Valves are linear-clavate with a tumid center.
The headpole is narrow and the footpole is rounded. Distinctly punctate striae are radiate and strongly radiate at the footpole. The axial area is narrow with a weakly undulate, laterally expanded raphe. The central area is laterally expanded opposite the stigma. Deflected internal proximal raphe ends are conspicuous.