Eunotia bidens

Ehrenb. 1943      Category: Eunotioid
SYNONYM(S): Eunotia praerupta var. bidens (Ehrenb.) Grunow 1880 

Eunotia bactriana


Eunotia bidentula

LM scalebar = 10 µm = 40 pixels.


Contributor: David R.L. Burge | Mark Edlund - June 2015
Length Range: 47-60 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


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.

Original Description

Author: Ehrenb. 1843
Length Range: µm
Striae in 10 µm:

Original Description

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

Original Images

Cite This Page:
Burge, D., and Edlund, M. (2015). Eunotia bidens. In Diatoms of the United States. Retrieved April 22, 2018, from

Species: Eunotia bidens

Contributor: David R.L. Burge | Mark Edlund

Reviewer: Paula Furey


Antoniades, D., Hamilton, P.B., Douglas, M.S.V. and Smol, J.P. (2008). Diatoms of North America: The freshwater floras of Prince Petrcik, Ellef Ringnes and northern Ellesmere Islands from the Canadian Arctic Archipelago. Iconographia Diatomologica 17.

Burge, D.R.L. (2014). Relations of water quality, land use buffers, and diatom communities of connected depressions within the Cache River Watershed, Arkansas, USA. M.S. Thesis. Arkansas State University, Jonesboro, Arkansas. 141 pp.

Ehrenberg, C.G. (1843). Verbreitung und Einfluß des mikroskopischen Lebens in Süd- und Nord-Amerika. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin, 1841: 291-445, 4 Tafel.

Furey, P.C., Lowe, R.L. and Johansen, J.R. (2011). Eunotia Ehrenberg (Bacillariophyta) of the Great Smoky Mountains National Park, USA. Bibliotheca Diatomologica 56: 1-134.

Lange-Bertalot, H., Bak, M., Witkowski, A. and Tagliaventi, N. (2011). Eunotia and some related genera. Diatoms of the European Inland Waters and Comparable Habitats. 6: 747 pp.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia bidens CAS

North American Diatom Ecological Database (NADED)


Autecology Discussion

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.