Image © Alfred van Geest
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.
Images © Alfred van Geest
Image © Henk Schulp