Krammer 2002 Category: Asymmetrical biraphid
BASIONYM: Cocconema pachycephalum Rabenhorst 1861
Contributor: Loren Bahls - April 2016
Length Range: 26-47 µm
Width Range: 7.6-11.2 µm
Striae in 10 µm: 9-12 in the valve center, up to 14 at the apices
Valves are dorsiventral with rounded ends. The dorsal margin is strongly arched; the ventral margin is weakly concave with a tumid center, becoming nearly flat in smaller specimens. The central area is wider than the axial area and elliptic. The raphe is distinctly lateral, becoming reverse-lateral near the proximal ends and filiform near the terminal ends. Proximal raphe ends are deflected ventrally and terminate in weakly inflated pores. Distal raphe ends are deflected dorsally at a 45 degree angle. Striae are radiate, becoming more strongly radiate near the apices. Striae are distinctly punctate with areolae that number 24-28 in 10 µm. Stigmata are lacking.
Basionym: Cocconema pachycephalum
Author: Rabenhorst 1861
Length Range: 25-59 µm
Width Range: 8-12 µm
Striae in 10 µm: 8-11(12) at valve center, 13-15 near the ends
Krammer, K. (2002). The genus Cymbella. Diatoms of Europe. Diatoms of the European Inland Waters and Comparable Habitats 3: 1-584.
Rabenhorst, L.G. (1861). Die Algen Europa’s Forsetzung der algen Sachsens, resp. Mittel-Europa’s. Decades 3-4, numbers 1021-1040. Dresden.
This taxon is widespread in the western US where its preferred habitats are springs and small lakes and streams. The five larger specimens shown here were collected from a small prairie stream in eastern Montana; the two smallest specimens are from a pothole lake in North Dakota and a small stream in southern California. The pH values of these waters range from 7.81 to 9.00 and specific conductance values range from 1693 to 7700 µS/cm. Unlike C. alpestris, C. hantzschiana is not restricted in distribution to glaciated regions and may also be found in more southerly, unglaciated habitats. Krammer (2002) reports that C. hantzschiana is widespread in temperate regions in oligo- to mesotrophic waters with an average electrolyte content.
Iron Spring, Carter County, Montana: home of Cymbella hantzschiana
Credit/Source: Loren Bahls