• Category
  • Length Range
    37-51 µm
  • Width Range
    14.2-18.8 µm
  • Striae in 10 µm
    8-10 in the valve center, 12-15 at the apices
  • Reported As
    Eunotia serra var. diadema (Patrick and Reimer 1966)
    Eunotia serra var. tetraodon (Krammer and Lange-Bertalot 1991)



Valves are highly arched. The dorsal margin has a constant 4 bluntly pointed undulations. Terminal undulations are distinct from and don't coalesce into the apices. The ventral margin is concave and follows the same curvature as the dorsal margin. The apices are wider than the undulations and obtusely rounded. Distal raphe ends lie along the valve face very close and parallel to each end. Striae are radiate throughout and of two types: complete striae that extend the full width of the valve and short striae that occur only along the dorsal margin. Short striae are more numerous in the undulations where they fill the gaps between complete striae. A fine transparent line runs close and parallel to the ventral margin. Striae on either side of this line may be continuous or displaced. Areolae in the striae are easily resolved in LM and number 20-25 in 10 µm.

Two morphotypes are present in the United States: The morphotype illustrated here (Morphotype I) and one in which the two central undulations are broadly rounded and the two outer undulations are acutely rounded (Morphotype II; see plate 10, figs. 6-10 in Werum & Lange-Bertalot 2004 and plate 105, figs. 5-9 in Lange-Bertalot et al. 2011).


Eunotia tetraodon has been collected from several ponds and small lakes in the Northern Rockies, where it is associated with aquatic vegetation. These waters all have low electrical conductance (range 19-31 µS/cm) and circumneutral to somewhat alkaline pH (range 5.50-8.81). Lange-Bertalot et al. (2011) report E. tetraodon as an infrequent component of the Holarctic flora in boreal and alpine regions of North America and Eurasia.

Drosera  Pond
Credit: Loren Bahls
Drosera Pond at Indian Meadows Research Natural Area, Helena National Forest, Montana.

Original Description

  • Author
    Ehrenb. 1838

Cite This Page

Bahls, L. (2012). Eunotia tetraodon. In Diatoms of North America. Retrieved May 20, 2024, from https://diatoms.org/species/eunotia_tetraodon


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Eunotia tetraodon 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.