Østrup 1910 Category: Asymmetrical biraphid
SYNONYM(S): Cymbella helvetica var. compacta (Østrup) Hustedt 1955
REPORTED AS: Cymbella helvetica (Krammer and Lange-Bertalot 1986, figs 133: 4, 5)
Contributor: Loren Bahls - April 2016
Length Range: 46-78 µm
Width Range: 11.4-15.3 µm
Striae in 10 µm: 9-11
Valves are dorsiventral with an arched dorsal margin and a slightly convex to nearly flat ventral margin. The apices are rounded and may become weakly protracted in larger specimens. The axial area is narrow and positioned just ventral of the valve mid line. The central area is small and elliptic in shape, or absent. Four to eight elongated areolae present at the proximal ends of median ventral striae. The raphe is lateral, becoming filiform near the proximal and terminal ends. Proximal raphe ends are hooked toward the ventral margin. Terminal raphe fissures are deflected dorsally at a 45 degree angle. Striae are radiate, becoming parallel, and then convergent near the apices. The striae continue around the valve apices. Areolae are distinct in LM and number 22-25 in 10 µm.
Author: Østrup 1910
Length Range: 29 µm
Width Range: 12 µm
Striae in 10 µm: 11
Krammer, K. (2002). The genus Cymbella. Diatoms of Europe. Diatoms of the European Inland Waters and Comparable Habitats 3: 1-584.
Østrup, E. (1910). Danske Diatoméer. C.A. Reitzels Boghandel, Kjøbenhavn. 323 pp., 5 pls.
Krammer (2002) reports Cymbella compacta to be widespread in eutrophic habitats with pH above 7. The specimens shown on this web page are from two streams in the Black Hills of western South Dakota. Geologically and ecologically, the Black Hills are considered an “island range” of the middle Rocky Mountains.
Little Spearfish Creek, Black Hills, South Dakota: home of Cymbella compacta
Credit/Source: Loren Bahls