Gomphonema gibba

Valves are lanceolate-clavate and slightly asymmetric to the apical axis. The valve tapers evenly from the center to the headpole, but more markedly to the footpole. The footpole is often slightly bent. The apices of the headpole and footpole are similar in width. The axial area is narrowly lanceolate. Striae are weakly radiate at the center valve, becoming nearly parallel at the headpole and strongly radiate at the footpole. A single stigmoid is present in line with the median stria on one side of the valve. The raphe is lateral. An apical porefield is present at the footpole. Girdle bands have a single to double row of poorly arranged areolae. Length:width is 4.4 (n=17).

The specimens presented here are of the holotype population from the Escambia River, Florida. This slide was examined by Patrick and Reimer (1975) and illustrated in a line drawing. The illustration appears to have more marked tapering from the center of the valve to the headpole and more protracted apices than the specimens we observed on the holotype slide. By examining a number of specimens on the slide, we extended the size range of G. gibba previously reported by Wallace (1960, 36 μm) and Patrick and Reimer (1975, 36-39 μm).

Specimens with protracted apices at the headpole and lower length to width ratio have been reported as G. gibba. Further analysis is needed to understand the variability in valve shape and ultrastructure, as well as the distribution of this taxon.