Hyalotheca dissiliensimage © Wim van Egmond

A number of filaments of Hyalotheca dissiliens in which mucous sheaths are clearly visible.

cell size (L x B): ca 18 x 25 µm



Desmid of the month
May 2003

Hyalotheca dissiliens

Hyalotheca dissiliens is a colonial, filamentous desmid, rather commonly occurring in all kinds of standing freshwaters, provided that those are not too acid/oligotrophic. Despite its wide distribution the species under discussion is frequently overlooked. Particularly on a superficial view, Hyalotheca may be easily confused with other, non-Conjugatophycean filamentous green algae. The reason is that cells hardly show any morphological differentiaton, such as a distinct sinus, which is characteristic of most desmid species. Moreover, cells join each other across almost their total breadth so that it looks as if we are dealing with a true (parenchymatic) filament rather than with a filamentous colony. Actually, cellular constitution of two semicells appears predominantly from the presence of two large, axile, radiating chloroplasts (one in each semicell). Only on closer inspection a very slight median constriction of the cell is to be distinguished.

Cell filaments of Hyalotheca dissiliens use to be enclosed by  a thick mucilage sheath. Such a sheath contributes to the colonial coherence and increases the chance of dispersal as the filaments readily stick to migratory water fowl, insects etc.

Detail of cell filament
image © Frantisek Hindák

Detail of cell filament. In the upper cells a slight median constriction (sinus) is to be seen.

Cell filament of Hyalotheca dissiliens. The enclosing mucilage sheath (in this picture hardly visible) is about as thick as half the cell breadth.