• Category
  • 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.


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  Or Orsnw1010 2191
Credit: Kirsten Gallo, Siuslaw National Forest
Snow Creek, Deschutes County, Oregon.

Original Description

  • Author
    Krammer 2002
  • Length Range
    48-121 µm
  • Width
    20-26 µm
  • Striae in 10µm
    7-11 at the valve center, up to 12 at the apices

Original Images

Cymbella perfossilis orig desc
Cymbella perfossilis orig illus
Cymbella perfossilis orig descr

Cite This Page

Bahls, L. (2016). Cymbella perfossilis. In Diatoms of North America. Retrieved July 19, 2024, from https://diatoms.org/species/cymbella_perfossilis


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Cymbella perfossilis from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.