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Psammothidium semiapertum

(Hust.) Aboal in Aboal, Alvarez-Cobelas, Cambra and Ector 2003      Category: Monoraphid
BASIONYM: Cocconeis semiaperta Hust. 1945
SYNONYM(S): Achnanthes hintzii Lange-Bert. and Krammer 

Psammothidium scoticum


Psammothidium subatomoides

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - July 2011
Length Range: 9-10 µm
Width Range: 4.4-5.2 µm
Striae in 10 µm: 22-24


Valves are elliptic. Raphe valve has a narrow linear axial area and a transversely rectangular central area. The raphe is filiform and straight with slightly expanded, almost straight or very slightly deflected external distal and proximal ends. Internal proximal raphe ends are deflected to opposite sides. Internal distal ends terminate in small helictoglossae. The apheless valve has a narrow linear axial area and a transversely rectangular central area that may be symmetric, or slightly asymmetric. Striae are uniseriate. Areolae are isodiametric and number 25 in 10 μm. There are 5-7 areolae in each central stria.

Note that specimens from the type material from Europe have slightly larger valves (about 6 μm wide) and more distinctly asymmetric central area on rapheless valve than specimens from the U.S. This species is, however, extremely rare in the type material and at present it is not possible to determine whether specimens from Europe and North America belong to the same species.

Original Description

Basionym: Cocconeis semiaperta
Author: Hust. 1945
Length Range: 10 µm
Width Range: 6 µm
Striae in 10 µm: 25

Original Description

Cocconeis semiaperta n. sp. - Schalen breit elliptisch, um 10 µ lang, etwa 6 µ breit. Raphenschale mit gerader, fadenförmiger Raphe, Axialarea sehr eng, Zentralarea einseitig bis fast an den Schalenrand erweitert. Transapikalstreifen durchweg radial, etwa 25 in 10 µ zart punktiert, Punkte in unregelmäßig welligen Längslinien, die annähernd in derselben Entfernung stehen wie die Transapikalstreifen. Raphenlose Schalen mit sehr schmal lanzettlicher Axialarea, Zentralarea einseitig bis an den Schalenrand er- weitert, Struktur der Zellwand wie an der Raphenschale.Taf. XXXIX Abb. 1-3. Plitvicer Seengebiet, sehr selten in einem Wasserfall und an litoraler Chara. - Besonders charakteristisch durch die Form der Zentralarea und mit keiner anderen Art zu verwechseln.

Original Images

Cite This Page:
Potapova, M. (2011). Psammothidium semiapertum. In Diatoms of the United States. Retrieved May 25, 2018, from

Species: Psammothidium semiapertum

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


Aboal, M., Alvarez-Cobelas, M., Cambra, J. and Ector, L. (2003). Floristic list of non marine diatoms (Bacillariophyceae) of Iberian Peninsula, Balearic Islands, and Canary Islands. Updated taxonomy and bibliography. In: A. Witkowski (ed.), Diatom Monographs. A.R.G. Gantner Verlag K.G., 4: 639 pp.

Krammer, K. and Lange-Bertalot, H. (2004). Bacillariophyceae 4. Teil: Achnanthaceae, Kritische Erganzungen zu Navicula (Lineolatae), Gomphonema Gesamtliteraturverzeichnis Teil 1-4 [second revised edition]. In: H. Ettl et al., Suesswasserflora von Mitteleuropa. Spektrum Akademischer Verlad Heidelberg, 468 pp.

Potapova, M. (2012). New species and combinations in monoraphid diatoms (Family Achnanthidiaceae) from North America. Diatom Research 27(1): 29-42. doi:10.1080/0269249X.2011.644636

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Psammothidium semiapertum CAS

North American Diatom Ecological Database (NADED)

NADED ID: 186020

Autecology Discussion

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Psammothidium semiapertum

EMAP Response Plots

Psammothidium semiapertum

EMAP citations

Results are published in:

Johnson, T., Hermann, K., Spaulding, S., Beyea, B., Theel, C., Sada, R., Bollman, W., Bowman, J., Larsen, A., Vining, K., Ostermiller, J., Petersen, D. Hargett, E. and Zumberge, J. (2009). An ecological assessment of USEPA Region 8 streams and rivers. U.S. Environmental Protection Agency Region 8 Report, 178 p.

Stoddard, J. L., Peck, D. V., Olsen, A. R., Larsen, D. P., Van Sickle, J., Hawkins, C. P., Hughes, R. M., Whittier, T. R., Lomnicky, G. A., Herlihy, A. T., Kaufman, P. R., Peterson, S. A., Ringold, P. L., Paulsen, S. G., and Blair, R. (2005). Environmental Monitoring and Assessment Program (EMAP) western streams and rivers statistical summary. U.S. Environmental Protection Agency Report 620/R-05/006, 1,762 p.

Stoddard, J. L., Peck, D. V., Paulsen, S. G., Van Sickle, J., Hawkins, C. P., Herlihy, A. T., Hughes, R. M., Kaufman, P. R., Larsen, D. P., Lomnicky, G. A., Olsen, A. R., Peterson, S. A., Ringold, P. L., and Whittier, T. R. (2005). An ecological assessment of western streams and rivers. U.S. Environmental Protection Agency Report 620/R-05/005, 49 p.