Visit us at

Diatoms of the United States is now known as Diatoms of North America.
This site has been redesigned and updated, and will be closing soon.

Rossithidium pusillum

(Grunow) Round and Bukht. 1996      Category: Monoraphid
BASIONYM: Achnanthes pusilla Grunow 1880
SYNONYM(S): Achnanthes pusilla Grunow in Cleve and Grunow 

Rossithidium petersenii


Scoliopleura peisonis

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - May 2009
Length Range: 10-16 µm
Width Range: 3.1-4.1 µm
Striae in 10 µm: 20-24


Valves linear or linear-elliptical with rounded ends, 3.1-4.1 µm wide, 10-16 µm long. Raphe valve with narrow axial area and with small round or irregular central area. Terminal raphe fissures absent. Raphe straight, filiform. Central raphe endings curved to opposite sides internally. Rapheless valve with narrow linear axial area without a central area or with a very small asymmetrical central area. Striae uniseriate, slightly radiate, one or two striae in the middle portion of the raphe valve are thicker than the rest, 20-24 in 10 µm. External openings of areolae are isodiametric or slightly elongated transapically. Each stria in the middle part of the valve contains 4-5 areolae. The valve mantle bears one row of areolae.

Original Description

Basionym: Achnanthes pusilla
Author: Grunow 1880
Length Range: 13-17 µm
Width Range: 3–4 µm
Striae in 10 µm: 18-23 in 10 µm

Original Description

Schaalen linear mit abgerundeten Enden. Querstreifen der Overschaale fast parallel, der Unterschaale schwach radial, die mittelsten entfernter und starker, 18-23 in 0.01 mm. Schaalen 0,013-0,017 mm. lang, 0.003-0,004 mm breit. Finshoe, Norwegen. Nordstedt.

Original Images

Cite This Page:
Potapova, M. (2009). Rossithidium pusillum. In Diatoms of the United States. Retrieved May 22, 2018, from

Species: Rossithidium pusillum

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


Cleve, P.T. and Grunow, A. (1880). Beiträge zur Kenntniss der Arktischen Diatomeen. Kongliga Svenska-Vetenskaps Akademiens Handlingar, 17(2): 121 pp., 7 pls.

Round, F. E. and Bukhtiyarova, L. (1996). Four new genera based on Achnanthes (Achnanthidium) together with a re-definition of Achnanthidium. Diatom Research 11: 345-361.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA
Original INA

California Academy of Sciences (CAS)

Rossithidium pusillum CAS

North American Diatom Ecological Database (NADED)

NADED ID: 189003

Autecology Discussion

As other monoraphid diatoms, Rossithidium pusillum is only slightly motile. Coldwater, oligotraphentic species.

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

Rossithidium pusillum

EMAP Response Plots

Rossithidium pusillum

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.