Contributor: Loren Bahls - May 2016
Length Range: 27-65 µm
Width Range: 8.8-13.0 (initial valve) µm
Striae in 10 µm: 9-13 dorsal, 12-14 ventral
Valves are dorsiventral and rhombic-lanceolate with acutely rounded apices. The dorsal margin is strongly arched; the ventral margin is weakly convex with a tumid center. The axial is relatively wide. The central area is a somewhat wider than the axial area. The raphe is distinctly lateral. The raphe is weakly lateral, with ventrally deflected proximal raphe ends. The proximal raphe teminates with slightly inflated pores. Distal raphe fissures are deflected dorsally. Striae are radiate, becoming more strongly radiate near the valve apices. Areolae are distinct in LM and number 22-26 in 10 µm. A stigma is absent.
Note that using the optics of the time, Østrup (1910) perceived a single isolated stigma on the ventral side of the central nodule, hence the name stigmaphora or “stigma-bearing”. Using modern optics, Krammer (2002) was not able confirm the presence of a stigma on the type specimens, nor has a stigma been found in any of the other populations that have been examined.
Author: Østrup 1910
Length Range: 56 µm
Width Range: 14 µm
Striae in 10 µm: 7-8
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.
The images of Cymbella stigmaphora on this web page are from a mountain stream and a mountain lake in northwestern Montana. The lake, Lower Saint Mary Lake on the Blackfeet Indian Reservation, has a pH of 8.00 and conductivity of 143 µS/cm. Besides the type locality in Denmark, Krammer (2002) reports this species from mesotrophic lakes in the lower Alps.