Krammer 2003 Category: Asymmetrical biraphid
BASIONYM: Cymbopleura frequens Krammer 2003
REPORTED AS: Cymbella amphicephala (Hustedt 1944 in Schmidt et al. 1874-1959, figs 377: 31-34)
Contributor: Loren Bahls - September 2015
Length Range: 20-44 µm
Width Range: 7.5-9.0 µm
Striae in 10 µm: 12-14 in the valve center, up to 16 near the apices
Valves are lanceolate, slightly dorsiventral and subtly triundulate with apiculate to rostrate apices. The dorsal margin is arched; the ventral margin is more weakly arched to almost straight. The axial area is narrow and linear-lanceolate, narrower at the ends and widening gradually to merge with a reduced and irregular central area. The central area that is barely wider than the axial area, or maybe wanting altogether. The raphe is weakly lateral and becomes filiform toward the proximal and distal ends. Proximal raphe ends are weakly expanded and tipped towards the ventral margin. Distal raphe ends are deflected dorsally. Striae are weakly radiate throughout and very finely punctate. Areolae in the striae number about 35 in 10 µm.
Basionym: Cymbopleura frequens
Author: Krammer 2003
Length Range: 14.0-38.0 µm
Width Range: 6.4-8.8 µm
Striae in 10 µm: 11-14 at the valve center, up to 15 near the apices
Valves not or only very slightly dorsiventral, subelliptical-lanceolate, dorsal and ventral margins moderately arched, ends apiculate to rostrate protracted. Length 14-38 µm, breadth 6.4-8.8 µm, maximum length/breadth ratio 4.8. Axial area narrow, linear, narrowing slightly towards the ends, almost in the median line of the valve. Central area an irregular, asymmetric space of different extent. Raphe slightly lateral, narrowing towards the proximal and distal ends. Proximal raphe ends slightly expanded and somewhat ventrally tipped, terminal fissures comma-shaped and dorsally deflected. Striae slightly radiate throughout, irregularly arranged around the central nodule, indistinctly punctate-lineate. Striae in the middle portion (dorsal) 11-14/10 µm, up to 15/10 µm towards the ends, puncta 30-36 (40)/10 µm.
Krammer, K. (2003). Cymbopleura, Delicata, Navicymbula, Gomphocymbellopsis, Afrocymbella. Diatoms of Europe. Diatoms of the European Inland Waters and Comparable Habitats 4: 1-530.
Schmidt, A. (-). (1874-1959). Atlas der Diatomaceen-Kunde, von Adolf Schmidt, continued by Martin Schmidt, Friedrich Fricke, Heinrich Heiden, Otto Muller, Friedrich Hustedt. Reprint 1984, Koeltz Scientific Books, Konigstein, 480 plates.
Cymbopleura frequens prefers oligotrophic to mesotrophic waters with moderate electrolyte content (Krammer 2003). The specimens shown here are from streams in western South Dakota (images 1-5) and Glacier National Park, Montana (image 6).