Eunotia lewisii

Siver and Hamilton 2009      Category: Eunotioid

Eunotia kociolekii


Eunotia macroglossa

LM scalebar = 10 µm = 40 pixels.


Contributor: Jen Beals - February 2012
Length Range: 35-107 µm
Width Range: 5.2-6.8 µm
Striae in 10 µm: 18.0-19.5


Valves are depressed on the ventral margin between the proximal raphe fissures. The dorsal margin is parallel to ventral margin, becoming slightly convex on shorter valves. Small spines are present along the dorsal margin, extending to the valve apices, but the spines are not distinguishable under LM. Valve apices are rostrate. Striae are regularly spaced and parallel, except at the apices where they become radiate distal to the terminal raphe fissures. Striae continue across the mantle. Areolae are small, circular and evenly spaced, 40-44 in 10 µm. The proximal raphe originates close to the mantle margin and continues straight on the ventral mantle, curving strongly across the valve apices towards the dorsal margin. Internally, the raphe terminates with prominent helictoglossae that are set in a thickened ridge continuing to the dorsal margin. One rimoportula is present near the base of the mantle at valve apex, parallel with the apical striae.

Note: Stria density in the original description was erroneously reported as 20-25 in 10 µm. Stria density of isotype specimen is 18 in 10 µm (per P. Hamilton).

Original Description

Author: Siver and Hamilton 2009
Length Range: 44-112 µm
Width Range: 5.5-6.5 µm
Striae in 10 µm: 20-25

Original Description

Valves are dorsi-ventral, elongate, with offset broadly rounded and slightly rostrate apices (Figs. 1–5). The ventral margin is straight and parallel with the dorsal margin over most of the valve, then extends outward slightly at the point where the raphe begins and where the apices start to constrict along the dorsal margin. The extended section is more noticeable on longer valves. The ventral valve margin is thickened, often forming a small continuous ridge (Figs. 8–10). A row of small spines can be found on the costae along the dorsal margin (Fig. 11), but these can be reduced or even absent on some specimens. The striae are evenly spaced and parallel over most of the valve; at the apices the striae are denser and radiate away from the terminal hyaline area onto the mantle (Figs. 8–10 and 12). Areolae are small, circular, closely spaced and not occluded on either the external nor internal surfaces (Figs. 8–13). The proximal end of the raphe commences about midway down the mantle, runs relatively straight and parallel to both margins, then curves up onto the valve face about 3 µm from the apex (Figs. 8–10). The distal raphe fissure terminates as a small pore about 1/4 the way across the valve face (Fig. 8). The raphe often interrupts the ridge on the ventral margin (Fig. 8). Internally where the distal end of the raphe terminates, a large, solid, thickening extends from the ventral mantle, across the valve face and terminates close to or at the dorsal margin (Figs. 6, 7, and 11–13). The thickening is usually smooth and hyaline. The distal end of the raphe curves up onto the proximal side of the thickened structure and terminates midway across the valve face as a small swollen helictoglossa (Figs. 12–13). The lower margin of the mantle is thickened, especially around the apices (Figs. 12 and 13). A single well-developed rimoportula, positioned parallel with the apical axis, is present near the base of the mantle at the very apex (Figs. 11 and 13). Valves ranged in size from 44–112 µm long x 5.5–6.5 µm wide with a striae density of 20–25/ 10 µm.

Original Images

Cite This Page:
Beals, J. (2012). Eunotia lewisii. In Diatoms of the United States. Retrieved April 19, 2018, from

Species: Eunotia lewisii

Contributor: Jen Beals

Reviewer: Sarah Spaulding


Furey, P.C., Lowe, R.L. and Johansen, J.R. (2009). Teratology in Eunotia taxa in the Great Smoky Mountains National Park and description of Eunotia macroglossa sp. nov. Diatom Research 24(2): 273-290. 10.1080/0269249X.2009.9705802

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.

Siver, P.A, Hamilton, P.B. and Pelczar, J. (2009). New species of freshwater diatoms from acidic localities along the Atlantic Coastal Plain of the United States. Botany 87: 409-427. doi:10.1139/B09-015

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia lewisii CAS

North American Diatom Ecological Database (NADED)

NADED ID: 33370

Autecology Discussion

Only known from moderately acidic ponds and lakes.