Taxon Account

Cocconeis placentula Ehrenberg; 1838; 194

Key references


Elliptic; raphe valve concave, rapheless valve convex, flexed in girdle view.

Valves isopolar, bilaterally symmetrical.

Frustules heterovalvar.

On raphe valve striae comprising small dot-like areolae, slightly radiate in the valve centre, becoming more radiate towards the valve ends. Striae are interrupted towards the margin by a raised siliceous rim; on rapheless valve striae comprising transapically elongate areolae which can appear doubled or trippled because the external areola openings are much wider than the internal openings, the areolae form slightly irregular, curved longitudinal lines.

Axial area
On raphe valve narrow linear, straight, terminating at marginal ridge; on rapheless valve wider axial area.

Central area
On raphe valve small circular central area; on rapheless valve not distinct from axial area.

Straight with slightly expanded proximal and distal ends, positioned close together; terminal ends straight, ending at ridge.

SEM morphology
Areolae on the rapheless valve long transapical slits, with much smaller round internal openings.

Valve surface of rapheless valve with small circular depressions.


References are given in chronological order.

Ehrenberg C.G. 1838. Die Infusionsthierchen als vollkommene Organismen. Ein Blick in das tiefere organische Leben de Natur. Verlag von Leopold Voss, Leipzig. 1-xvii, 1-548 pp; 1-64 pls Illustrations; Morphology
Monnier O., Rimet F., Bey M., Chavaux R., Ector L. 2007. Sur l’identité de Cocconeis euglypta Ehrenberg 1854 et C. lineata Ehrenberg 1843 – Une approche par les sources historiques. Diatomania. 11: 30-45. Biology; Illustrations; Morphology
Jahn R., Kusber W.-H., Romero O.E. 2009. Cocconeis pediculus EHRENBERG and C. placentula EHRENBERG var. placentula (Bacillariophyta): Typification and taxonomy. Fottea. 9(2): 275-288. Description; Morphology; Type Illustration; Illustrations
This page should be cited as:

Jüttner I., Jüttner I. Cocconeis placentula Ehrenberg; 1838; 194. In: Jüttner I., Carter C., Cox E.J., Ector L., Jones V., Kelly M.G., Kennedy B., Mann D.G., Turner J. A., Van de Vijver B., Wetzel C.E., Williams D.M.. Freshwater Diatom Flora of Britain and Ireland. Amgueddfa Cymru - National Museum Wales. Available online at [Accessed:  ].

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Record last modified: 27/12/2020