• Category
  • Length Range
    33–110 µm
  • Width Range
    3.1–4.7 µm
  • Striae in 10 µm
    11–16 at center of the valve, 15–19 near the apices
  • Synonyms
    Eunotia bilunaris (Ehrenb.) M.G.M.Souza in M.G.M.Souza and Moreira-FIlho 1999



Valves are arcuate, with convex dorsal and concave ventral margins. Margins are parallel near the apices. In some specimens, the ventral margins are slightly swollen near the transapical axis. Apices are rounded in larger specimens, becoming more acute in smaller speciments. Helictoglossae are positioned near the apices, along the ventral margin. The distal raphe end curves from the ventral margin onto the valve face and then back towards the center of the valve. Striae are spaced evenly, becoming more dense near the apices. Areolae are fine and not visible in LM.


Eunotia bilunaris has wide geographic and habitat distribution in North America. It has been reported from epiphytic and epilithic site of the Great Smoky Mountains (Furey et al. 2011), wetlands (Burge 2014), lakes (Antoniades et al. 2008, Siver and Hamilton), and in rivers of Québec-Labrador (Fallu et al. 2000).

Antoniades et al. (2008) observed E. bilunaris in less than 2% abundance occurring benthic in small lakes and ponds of Prince Patrick Island (Northwest Territories, Canada), with the following water chemistry: pH 7.1-8.0, conductivity 40-97 µS/cm, and 4.79-10.34 DOC (mg/L). Siver and Hamilton (2011) observed E. bilunaris occurring in ponds and canals of the Pocosin NWR (North Carolina), with a pH 4.5+/-1.2 and TP 37+/-18 µg/L. Burge (2014) observed E. bilunaris populations occurring <1% to 48% relative abundance in assemblages with E. formica, E. metamonodon, E. praeruptua, as well as species of Gomphonema, Navicula, and Pinnularia, in cypress-tupelo wetlands of the Cache River NWR (Arkansas) with the following water chemistry: 19.2–31.5oC, pH 5.18 –7.7, DO 0.1–7.7 mg/L, specific conductance 11.8–1358 µS/cm, Turbidity 3.9–628 NTU, Chlorophyll-a 0–167.3mg/L, NH3-N 0.1–16.1, NO3-N <0.1–0.8 mg/L, NO2-N 0–0.2 mg/L, TN 0.6–8.1 mg/L, TP <0.1–4.6 mg/L, and PO4-P <0.1–2.8 mg/L.

In Europe, E. bilunaris is found within moderately dystrophic waters with increased concentrations of sulfate (Alles et al. 1991).

Original Description

  • Basionym
    Synedra bilunaris
  • Author
    Ehrenb. 1832

Original Images

Synedra Bilunaris

EMAP Assessment

EMAP Distribution

Eunotia Bilunaris   Ehrenberg   Mills 10
Map 10

Response Plots

Eunotia Bilunaris   Ehrenberg   Mills

Citations & Links



Cite This Page

Burge, D, and Edlund, M. (2015). Eunotia bilunaris. In Diatoms of North America. Retrieved June 22, 2018, from https://diatoms.org/species/eunotia_bilunaris


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