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Diatoms of the United States is now known as Diatoms of North America.
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Eunotia tetraodon

Ehrenb. 1838      Category: Eunotioid

REPORTED AS: Eunotia serra var. diadema (Patrick and Reimer 1966) | Eunotia serra var. tetraodon (Krammer and Lange-Bertalot 1991) 

Eunotia tenella


Eunotia trinacria

LM scalebar = 10 µm = 40 pixels.


Contributor: Loren Bahls - July 2012
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


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).

Original Description

Author: Ehrenb. 1838
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Bahls, L. (2012). Eunotia tetraodon. In Diatoms of the United States. Retrieved May 22, 2018, from

Species: Eunotia tetraodon

Contributor: Loren Bahls

Reviewer: Paula Furey


Ehrenberg, C.G. (1838). Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben de Natur. erlag von Leopold Voss, Leipzig. pp. 1-xvii, 1-548, pls. 1-64.

Krammer, K. and Lange-Bertalot, H. (1991). Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (Eds.). Süsswasserflora von Mitteleuropa. 2(3): 1-576. Gustav Fisher Verlag, Stuttgart, Germany.

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.

Patrick, R.M. (1958). Some nomenclatural problems and a new species and a new variety in the genus Eunotia (Bacillariophyceae). Notulae Naturae 312: 1-15.

Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.

Werum, M. and Lange-Bertalot, H. (2004). Diatoms in springs, from Central Europe and elsewhere under the influence of hydrogeology and anthropogenic impages. Iconographia Diatomologica 13: 1-417.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia tetraodon CAS

North American Diatom Ecological Database (NADED)

NADED ID: 33272

Autecology Discussion

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, Indian Meadows Research Natural Area, Helena National Forest, Montana: home of Eunotia tetraodon.

Credit/Source: Loren Bahls