Placoneis gastrum

(Ehrenb.) Mereschk. 1903      Category: Symmetrical biraphid
BASIONYM: Pinnularia gastrum Ehrenb. 1843
SYNONYM(S): Navicula gastrum (Ehrenb.) Kütz. 

Placoneis explanata


Plagiotropis arizonica

LM scalebar = 10 µm = 40 pixels.


Contributor: James D. Woodell - June 2015
Length Range: 30-56 µm
Width Range: 15.9-20.0 µm
Striae in 10 µm: 7-9 near the center, up to 10 near the apices


Valves are elliptic, with broadly rounded to rostrate apices. Valves are usually slightly asymmetric to the apical axis. The axial area is narrow and the central area is irregular or transverse due to striae of variable length and arrangement. The raphe is simple, filiform, and slightly curved toward the secondary side of the valve. The proximal raphe ends are slightly expanded. The distal raphe ends are abruptly hooked at the valve mantle. Striae are strongly radiate, curved and irregularly shortened near the central area. Striae are distinctly uniseriate, widely spaced from one another and number between 6-10 in 10 μm. Areolae number 24-27 in 10 μm.

Original Description

Basionym: Pinnularia gastrum
Author: Ehrenb. 1843
Length Range: µm
Striae in 10 µm:

Original Description

P. gastrum, testula minor ventre late lanceolato, apicibus constrictis obtusis, parem productis, papillaribus. Icon!

Original Images

Cite This Page:
Woodell, J. (2015). Placoneis gastrum. In Diatoms of the United States. Retrieved April 25, 2018, from

Species: Placoneis gastrum

Contributor: James D. Woodell

Reviewer: Dennis Vander Meer


Cox, E.J. (2003). Placoneis Mereschkowsky revisited: resolution of several typification and nomenclatural problems, including the generitype. Bot. J. Linn. Soc. 141: 53–83. 10.1046/j.1095-8339.2003.00115.x

Ehrenberg, C.G. (1843). Verbreitung und Einfluß des mikroskopischen Lebens in Süd- und Nord-Amerika. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin, 1841: 291-445, 4 Tafel.

Mann, D.G. and Stickle, A. (1995). Sexual reproduction and systematics of Placoneis (Bacillariophyta). Phycologia 34: 74-86.

Mereschkowsky, C. (1903). Über Placoneis, ein neues Diatomeen-Genus. Beihefte zum Botanischen Centralblatt 15 (1): 81-88.

Links & ID's

Index Nominum Algarum (INA)


California Academy of Sciences (CAS)

Placoneis gastrum CAS

NCBI Genbank Taxonomy

Placoneis gastrum NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 194008

Autecology Discussion

Placoneis gastrum is generally epipelic in meso- to eutrophic and brackish freshwater lakes and streams (Cox 2003). Placoneis gastrum was a significant indicator of low total phosphorus and marginal total nitrogen in the Awash, Blue Nile, and Omo-Gibe river basins in Ethiopia (Beyene et al. 2013). It was originally described among marine algae from Vera Cruz, Mexico, but its presence there was not confirmed in a later study (Cox 2003). Populations of P. gastrum were found in the plankton in Lazy Lagoon and Beck’s Canal in West Lake Okoboji, Dickinson County, Iowa. It has also been found in Douglas Lake, Michigan, and many other sites around the world (Cox 2003).

Chloroplasts are single, usually positioned on one side of the cell opposite the nucleus, and consist of a lobed plate on each valve connected by a central bridge which contains a flat pyrenoid (Mann and Stickle 1995). The chloroplast and the pyrenoid are split during cytokinesis rather than dividing on their own before cell division, and these, along with the nucleus, are stationary during reproduction (Mann and Stickle 1995). The chloroplast structure was a defining part of Mereschkowsky’s original Placoneis description (Cox 2003), where he also stated that Placoneis was likely more closely related to Cymbella than to the naviculoids (Mann and Stickle 1995). Placoneis gastrum has been observed to occasionally form triplets for sexual reproduction connected by a single mucilage capsule (Mann and Stickle 1995).


Distribution of Placoneis gastrum in rivers of the continental U.S. based on the National Water Quality Assessment program. Retrieved 03 June 2015.

Credit/Source: USGS BioData

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

Placoneis gastrum

EMAP Response Plots

Placoneis gastrum

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.