Two cells of Gonatozygon monotaenium. Notice the cylindric shape (without a sinus). Notice also slightly dilated apices marked by somewhat produced, acutely rounded angles.

Cell dimensions (L x B) of larger cell: ca 280 x 12 µm


Desmid of the month
July 2006

Gonatozygon monotaenium

The genus Gonatozygon belongs to a separate family of placoderm desmids (Fam. Gonatozygaceae). Cells are elongate and but little desmid-like as a median constriction is wanting and semicell morphology is most simple. Chloroplasts, one or two per cell, are in the form of a plate, either simple or provided with a number of longitudinal ridges rendering them more or less stelloid in cross section. Under certain (less optimal?) conditions, however, chloroplasts take the form of an irregularly spiralled band. Frequently, cells are attached to each other to form filaments of variable length. Incidentally even whole webs may be formed much resembling those of the filamentous zygnematalean alga Mougeotia.

Cells of Gonatozygon monotaenium are elongate-cylindric and characterized by a finely granulate cell wall. In the Netherlands G. monotaenium is rather common in mesotrophic, slightly acidic or circumneutral water bodies. Zygospore formation, on the contrary, is rare.

Details of cell apex in different focus making clear that the produced apical angles are effected by the optical section of a ring-shaped apical extension of the cell wall.

some muaually linked cells mouse over images © Henk Schulp

Some mutually linked cells of G. monotaenium. Notice fine cell wall granulation.

Conjugated cells of G. monotaenium with a globular, smooth-walled zygospore in between.


mouse over images © Alfred van Geest

Extended web of G. monotaenium filaments (encountered in wintertime, in very shallow water)

mouse over:

Web of G. monotaenium in detail. Notice that chloroplasts in most of the cells are irregularly spiralled (more or less parietal like in the genus Genicularia).