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Fragilariforma bicapitata

(A.Mayer) D.M.Williams and Round 1988      Category: Araphid
BASIONYM: Fragilaria bicapitata A.Mayer 1917
SYNONYM(S): Neofragilaria bicapitata (A.Mayer) D.M.Williams and Round 

Fragilariforma acidobiontica


Fragilariforma constricta

LM scalebar = 10 µm = 80 pixels.


Contributor: Ian Bishop - August 2014
Length Range: 9-51 µm
Width Range: 2.9-5.5 µm
Striae in 10 µm: 11-15


Valves are linear to lanceolate with rostrate apices. Striae are irregularly spaced and do not align from opposite sides of the valve where they meet at the central sternum. The striae appear relatively thick, but areolae not visible in LM. Large apical porefields are present at both ends of the valve. Length to breadth ratio decreases with increasing valve length. In SEM, the striae are seen to be uniseriate. Two rimoportulae are present, one at each apex of the valve. Each rimoportula is aligned with the striae. Small marginal spines are present on each interstria. Spines continue around the valve apex, and are positioned on the apical porefields.

Original Description

Basionym: Fragilaria bicapitata
Author: A.Mayer 1917
Length Range: 17-32 µm
Striae in 10 µm: 13-15

Original Description

Original Images

Cite This Page:
Bishop, I. (2014). Fragilariforma bicapitata. In Diatoms of the United States. Retrieved May 20, 2018, from

Species: Fragilariforma bicapitata

Contributor: Ian Bishop

Reviewer: Eduardo A. Morales


Mayer, A. (1917). Beiträge zur Diatomeenflora Bayerns. Part I, A. Bacillariales aus dem Fichtelgebirge und angrenzenden Gebieten. B. Bacillariales aus dem Bayrischen Walde. Denkschriften der Koniglich-Baierischen Botanischen Gesellschaft in Regensburg 13: 1-99, pls. 1-8.

Williams, D.M. and Round, F.E. (1987). Revision of the genus Synedra Ehrenb. Diatom Research 1(2): 313-339.

Williams, D.M. and Round, F.E. (1988). Fragilariforma, nom. nov., a new generic name for Neofragilaria Williams & Round. Diatom Research 3: 265-267.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Fragilariforma bicapitata CAS

North American Diatom Ecological Database (NADED)

NADED ID: 192001

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

Fragilariforma bicapitata

EMAP Response Plots

Fragilariforma bicapitata

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.