• Category
  • Length Range
    46.7-60.0 µm
  • Width Range
    at the valve center: 8.5-10.5 µm
  • Striae in 10 µm
    9-12 in the valve center, 12-15 at the ends
  • Synonyms
    Eunotia praerupta var. bidens (Ehrenb.) Grunow 1880



Valves are weakly arcuate, with distinct, broadly rounded biundulate dorsal margins. The apices are subcapitate with ends that are obtusely rounded, 5.9-7.2 µm wide. Helictoglossae are present on the ventral margin, near the apices. The raphe curves onto the ventral mantle toward the center of the valve, terminating at ventral undulations 1/5 valve length from the ends. Transapical striae are nearly parallel, becoming curved near the ends. Shortened striae are infrequently present near the dorsal margin. A narrow sternum is present near the ventral margin, visible near raphe at the apices. Areolae visible in LM, occurring 28-31 in 10 µm. Internal openings of the areolae aligned in a narrow groove.


The distribution of E. bidens has been reported as ranging from the Arctic (Antoniades et al. 2008) to tropics, occurring in oligtraphentic, acidic waters of low conductivity (Lange-Bertalot et al. 2011). Eunotia bidens has commonly been found associated with bryophyte communities in swamps of the Mississippi River Delta (Burge 2014), and stream of Great Smoky Mountains National Park (Furey et al. 2011).

Burge (2014) found E. bidens occurring in less than 30% relative abundance among the epiphyton and benthos of cypress-tupelo wetlands with: 22.2–27.4 C, 5.6–7.4 pH, specific conductivity 71.2–834.0 µS/cm, 8.1–321.0 NTU, DO 0.1–7.7 mg/L, NO3-N 0.01–0.3 mg/L, NO2-N <0.001– 0.1 mg/L, orthophosphate 0.02–2.08 mg/L, and TP 0.11–3.93 mg/L. Other common species were Eunotia formica, E. bilunaris, E. metamonodon, and E. superbidens as well as species of Gomphonema, Navicula, Nitzschia, and Pinnularia.

Original Description

E. bidens, striata, ventre plano, dorso convexo medio exciso (bidentato), apicibus dilatatis truncatis. = E. Diodon apicibus truncatis.

  • Author
    Ehrenb. 1843

Original Images

Eunotia Bidens  Ehrenberg 1843

Cite This Page

Burge, D, and Edlund, M. (2015). Eunotia bidens. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/eunotia_bidens


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