Contributor: Loren Bahls - June 2016
Length Range: 70-138 µm
Width Range: 17.4-26.3 µm
Striae in 10 µm: 8-11 at the valve center, up to 12 near the apices
Valves are dorsiventral with a strongly arched dorsal margin. The ventral margin is weakly concave, with a slightly tumid center. Apices are broadly rounded, somewhat protracted in the smallest valves. The axial area is narrow. The central area is large and irregularly rounded. From 4-8 stigmata form a straight line on the ventral side of the central area, placed at some distance from the ends of the median ventral striae. In some specimens, there is an additional isolated stigma on the dorsal side of the central area. The raphe is lateral. Proximal raphe ends are hook-shaped and are deflected ventrally. Terminal raphe fissures are deflected dorsally at about 45 degrees. Striae are radiate throughout, more strongly radiate near the apices. Areolae are easily resolved in LM and number 16-20 in 10 µm.
Author: Krammer 2002
Length Range: 48-121 µm
Width Range: 20-26 µm
Striae in 10 µm: 7-11 at the valve center, up to 12 at the apices
Krammer, K. (2002). The genus Cymbella. Diatoms of Europe. Diatoms of the European Inland Waters and Comparable Habitats 3: 1-584.
Cymbella perfossilis is a “living fossil”. This species was described from fossil material collected near Terrebonne, Oregon, on the eastern slopes of the Cascade Mountains. Extant populations were recently found nearby in three Cascade Mountain streams. In one of these streams (Snow Creek, photo below), pH measured 7.63 and specific conductance measured 27 µS/cm.
Snow Creek, Deschutes County, Oregon: home of Cymbella perfossilis
Credit/Source: U. S. Forest Service