The beginner in the study of desmids may not at first realise that there are desmids that form filaments, some quite long filaments, and he/she may not always distinguish these from other algae that is filamentous. The majority of filamentous species of algae have continuous walls divided into cells by septa, for example the well known Spirogyra which is related to the desmids, as it also conjugates. (Fig.1 shows Spirogyra with the desmid Closterium moniliferum).

Examination of the desmid filaments will reveal that the cells are not contained in a continuous wall but are separate cells joined at their apices in some way, some tightly with no visible space between them, others have pads that join the cells leaving a space, others are loosely joined with interlocking processes. Some genera exude copious amounts of mucilage that appear to be instrumental in keeping the desmid cells attached.

The filamentous desmid genera/species most frequently found are Bambusina brebissonii and Hyalotheca dissiliens. Bambusina brebissonii Kütz (1849) is listed in early books as Gymnozyga moniliformis Her. (1841). There is only one species of the genus found in Britain; cells 25-35 µm long 15-23 µm broad, circular in apical view. Fig. 2 is a light microscope photomicrograph, figs. 3 & 4. SEM images. A complete cell is shown between the lines. In fig. 4. rows of evenly spaced small punctae can be seen.

Hyalotheca Bréb. ex Ralfs (1848): There are five British species (Fritsch 1927), H.dissiliens being the most abundant. (Fig.5 photographed in Indian ink to show the copious mucilage. Fig. 6 shows one cell broken away and seen in apical view.)

Photomicrographs of other genera/species of filamentous desmids will be shown later.

The light microscope photo’s are by the author, SEM photo’s are by Andrew Syred.

Reference
“A Treatise on the Freshwater Algae”  by G.S.West (1904) revised by F.E. Fritsch (1927), Cambridge University  Press.

All comments to the author Bill Ells are welcomed.

'Desmids that form filaments, part two' by the author is here.
 
 

Images

Fig.1. Spirogyra with the desmid Closterium moniliferum.

Fig. 2. Bambusina brebissonii Kütz (1849). Optical microscope.

Fig. 3. Bambusina brebissonii Kütz (1849). SEM image.

Fig. 4. Bambusina brebissonii Kütz (1849). SEM image, detail.

Fig. 5. Hyalotheca dissiliens Bréb. ex Ralfs (1848). In Indian ink to show mucilage.

Fig. 6. Hyalotheca dissiliens Bréb. ex Ralfs (1848).  One cell is shown broken away and seen in apical view.