Meridion circulare

(Grev.) C.Agardh 1831      Category: Araphid
BASIONYM: Echinella circularis Grev. 1831

Meridion anceps


Meridion circulare var. constrictum

LM scalebar = 10 µm = 80 pixels.


Contributor: Pat Kociolek - January 2011
Length Range: 17-80 µm
Width Range: 3-4 µm
Striae in 10 µm:


Frustules form fan-shaped colonies and are clavate in girdle view. Valves are linear-clavate and asymmetric to the transapical axis. Costae are present and run transversely across the valves. In many specimens illustrated here, the costae are only present towards the headpole, and are not present towards the footpole. A narrow sternum is present running the length of the valve. A single rimoportula is located near the headpole. Though rarely reported, Meridion species do possess a septum, and these were commonly seen in the material.

Williams (1985, p. 160) reports the breadth of M. circulare as 10-21 µm, while Patrick and Reimer (1966) give 4-8 µm.

Distribution: Meridion circulare is found across the US, in habitats flowing water and spring habitats.

Original Description

Basionym: Echinella circularis
Author: Grev. 1831
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Kociolek, P. (2011). Meridion circulare. In Diatoms of the United States. Retrieved April 24, 2018, from

Species: Meridion circulare

Contributor: Pat Kociolek

Reviewer: Rex Lowe


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.

Williams, D.M. (1985). Morphology, taxonomy and inter-relationships of the ribbed araphid diatoms from the genera Diatoma and Meridion (Diatomaceae: Bacillariophyta). Bibliotheca Diatomologica 8: 1-228.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Meridion circulare CAS

North American Diatom Ecological Database (NADED)

NADED ID: 45001

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

Meridion circulare

EMAP Response Plots

Meridion circulare

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.