Cocconeis placentula sensu lato

Ehrenb. 1838      Category: Monoraphid

Cocconeis pediculus


Cocconeis pseudothumensis

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova | Sarah Spaulding - January 2013
Length Range: 9-68 µm
Width Range: 7-32 µm
Striae in 10 µm: 20-24 on raphe valve, 15-25 on rapheless valve


Valves are elliptic to linear-elliptic and relatively flat. The raphe (R) valve has a narrow axial area and a small circular or oval central area. The raphe is straight and filiform. The distal raphe ends are straight and expanded externally. The proximal raphe ends are straight externally and slightly expanded. Internally, the proximal raphe ends are deflected to opposite sides. Striae are radiate and interrupted by a hyaline ring positioned close to the valve margin. The areolae are usually well distinguished under LM, 15-25 in 10 µm along a stria. The valvocopula attached to raphe valve has conspicuous fimbriae. The rapheless (RL) valve has a linear to linear-lanceolate axial area and radiate striae. The external openings of areolae are narrow, long transapical slits. The internal openings are comparatively shortened and are oval, or nearly round. There are 8-20 areolae in 10 µm along a stria in the RL valve.

The concept of Cocconeis placentula presented here is in the broad sense (sensu lato). We group several varieties (and species), including the nominate variety C. placentula var. placentula, C. euglypta and C. lineata. The reason for presenting such a wide concept of this species is the lack of clearly established differentiating criteria between these taxa in monitoring programs. There has been a great deal of confusion because the RL valve is needed to determine the variety or species; the R valves of the varieties appear to be indistinguishable. In our experience, neither original descriptions of these taxa, nor the descriptions available in the floras are sufficient to separate them with any degree of certainty. Jahn et al. (2009) initiated a study of type materials of Cocconeis, including that of the nominate variety of C. placentula. Recent work (Romero and Jahn 2013) provided lectotypification of C. lineata and C. euglypta, yet further studies are necessary to determine whether and how individual species within C. placentula sensu lato may be distinguished using morphological characters.

Original Description

Author: Ehrenb. 1838
Length Range: µm
Striae in 10 µm:

Original Description

  1. Cocconeïs Placentula, Kuchen-Schildchen. C. testula elliptica plana, margine abrupto, extus et intus laevis.Cocconéide Gâteau, à carapace elliptique plate, escarpée au bord, extérieurement et intérieurement lisse.Aufenthalt: Bei Berlin. Auf Vaucherien und Lemna-Wurzeln findet sica diese Form zuweilen sehr zahlreich bei Berlin. Ich sah sie auch am Byssus des Mytilus polymorplius. — Länge 1/120 Linie; Breite mehr als 2/3 der Länge; Höhe 1/4 bis 1/5 der Länge. Eine Abbildung konnte nicht mehr gegeben werden. (Vergl. Conferva pennatula, VAHL, Flora danica, T. 945. 1792.)

Original Images

Cite This Page:
Potapova, M., and Spaulding, S. (2013). Cocconeis placentula. In Diatoms of the United States. Retrieved April 22, 2018, from

Species: Cocconeis placentula

Contributor: Marina Potapova | Sarah Spaulding

Reviewer: Kalina Manoylov


Ehrenberg, C.G. (1838). Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben de Natur. erlag von Leopold Voss, Leipzig. pp. 1-xvii, 1-548, pls. 1-64.

Geitler, L. (1927). Somatische Teilung, Reduktionsteilung, Copulation und Parthenogenese bei Cocconeis placentula. Archiv für Protistenkunde 59: 506–549.

Geitler, L. (1932). Der Formwechsel der pennaten Diatomeen (Kieselalgen). Archiv für Protistenkunde 78: 1–226.

Geitler, L. (1958). Fortpflanzungsbiologische Eigentümlichkeiten von Cocconeis und Vorarbeiten zu einer systematischen Gliederung von Cocconeis placentula nebst Beobachtung an Bastarden. Österreichische Botanische Zeitschrift 105: 350–379.

Geitler, L. (1982). Die infraspezifischen Sippen von Cocconeis placentula des Lunzer Seebachs. . Algological Studies 30: 1–11.

Jahn, R., Kusber, W.H. and Romero, O.E. (2009). Cocconeis pediculus Ehrenberg and C. placentula Ehrenberg var. placentula (Bacillariophyta): Typification and taxonomy. Fottea 9(2): 275–288.

Romero, O. and Jahn, R. (2013). Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta). Diatom Research 28(2): 175-184. 10.1080/0269249X.2013.770801

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Cocconeis placentula CAS

NCBI Genbank Taxonomy

Cocconeis placentula NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 16004

Autecology Discussion


Light micrograph of living cells of Cocconeis placentula attached to a glass slide. Cells of Achnanthidium are also present. Chloroplasts are visible within the silica cell walls.

Credit/Source: Mark Edlund

Scannning electron micrograph of living cells of Cocconeis placentula attached to a rock. Note the mucilage pads present around a number frustules. The raphe valve is fixed to the substrate, while the rapheless valve faces up. Scale bar is equal to 50 µm.

Credit/Source: Sarah Spaulding

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

Cocconeis placentula

EMAP Response Plots

Cocconeis placentula

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.