(Grunow) Krammer 2002 Category: Asymmetrical biraphid
BASIONYM: Cocconema kamtschaticum Grunow in A. Schmidt 1875
Contributor: Loren Bahls - June 2016
Length Range: 64-102 µm
Width Range: 25.7-31.0 µm
Striae in 10 µm: 6-9
Valves are relatively broad, cymbelloid and semi-elliptic. Apices are bluntly rounded and weakly protracted. The dorsal margin is strongly arched; the ventral margin is slightly convex to nearly flat. The axial area is linear and a bit wider than the raphe. The central area is small and circular to elliptic in shape. A single large stigma is present between the proximal raphe ends. The raphe branches are lateral, becoming narrower near the proximal and distal ends. Proximal raphe ends terminate in bulbous central pores that are deflected slightly towards the ventral margin. Terminal raphe fissures are deflected dorsally at about 45º. Well developed porefields are present at both apices. Striae are radiate throughout. The dorsal and ventral striae in the central portion of the valve are variable in length. Areolae are very distinct in LM and number 10-12 in 10 µm. Areolae on the ventral side of the central area are elongate and triangular in shape.
This is a smaller, more compact form of C. mexicana with bluntly rounded and weakly protracted apices. It may occur in association with the nominate variety, but it is often the only variety of the species that is present.
Editor’s note: Users should be aware that this variety may represent small forms of the nominate species. We appreciate documentation and feedback on the occurrence of this taxon in North America.
Basionym: Cocconema kamtschaticum
Author: Grunow in A. Schmidt 1875
Length Range: 70-160 µm
Width Range: 25-32 µm
Striae in 10 µm: 6-9
Krammer, K. (2002). The genus Cymbella. Diatoms of Europe. Diatoms of the European Inland Waters and Comparable Habitats 3: 1-584.
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.
NADED ID: 23197
Cymbella mexicana var. kamtschatica has been collected from several creeks and rivers in the Northern Rocky Mountains of Montana and Idaho. The pH of these waters ranges from 7.90 to 8.55 and specific conductance ranges from 61 to 608 µS/cm. It may occur in association with the nominate variety, but often not. This variety was described from fossil material collected in Kamtschatka and has also been reported from the Colorado River (Krammer 2002).
Clark Fork River near Missoula, Montana: home of Cymbella mexicana var. kamtschatica