Studies on the diatom genus Stenopterobia (Bacillariophyceae) including descriptions of two new species

During an investigation of freshwater diatoms from highly acidic ponds scattered along the Atlantic Coastal Plain of North Carolina we encountered a large number of specimens from the genus Stenopterobia . All of the specimens were representative of straight, not sigmoidal-shaped, taxa and collectively ranged in length from ca. 10 µm to over 200 µm. In the process of making species determinations we examined type material for four species of Stenopterobia originally described by Lewis (1864) from Saco Pond, a small spring-fed waterbody nestled in the White Mountains of New Hampshire. The four species, Stenopterobia baileyi (Lewis) Brébisson ex Van Heurck, Stenopterobia anceps (Lewis) Brébisson ex Van Heurck, Stenopterobia delicatissima (Lewis) Brébisson ex Van Heurck, and Surirella intermedia Lewis (=Stenopterobia curvula (W. Smith) Krammer), were originally placed by Lewis within the genus Surirella. We examined seven permanent slides archived at the Academy of Natural Sciences of Philadelphia that contained material collected by Lewis. In addition, we collected new material from Saco Pond, including a sediment core, and examined these samples using SEM. We also examined type material for another species, Stenopterobia cuspidata (Hustedt) Vyverman, using SEM. We concluded that the North Carolina collections contained five species, two described as new ( Stenopterobia gracilis sp. nov. Siver & Camfield and Stenopterobia fusiformis sp. nov. Siver & Camfield), two representing organisms originally described by Lewis (S. baileyi and S. delicatissima), and the fifth recently described from Cape Cod ( Stenopterobia pseudodelicatissima Siver & Hamilton). New characters, including externally capped areolae, valve face coverings, and laterally opened girdle bands, are described for the genus. Lastly, lectotypes for three of Lewis’ taxa were selected.