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Phylum Chlorophyta, sub-phylum Chlorophyceae, order Zygnematales, fam. Zygnemataceae.
Mougeotia species are unbranched filamentous green algae. The cell wall is characteristically straight and parallel-sided (compare with Oedogonium, Microspora or Stigeoclonium, which sometimes have bulbous cells).
They have a single chloroplast in the form of an axial plate or ribbon which usually almost fills the length of the cell.
The chloroplast may be seen lying flat (horizontal) when seen through the microscope, or it may be twisted and can sometimes be seen as a narrow strip up the middle of the cell.
There are several pyrenoids which are starch containing bodies and can be revealed by staining with Lugol’s iodine (the starch turns black).
Unfortunately, many Mougeotia species are sensitive to iodine, and pressure, and the filaments may break up, so the iodine test should be performed after first examining the fresh material.
Mougeotia are members of the Zygnematales or Conjugales, which as the name suggests enjoy sexual reproduction; neighbouring filaments send out processes which fuse into a tube, then the cell contents pass into the conjugation tube and form the zygospore.
The appearance of the zygospore is used to identify to species, but this characteristic is rarely found in field material.
Many species show scalariform conjugation; many adjoining cells in the two filaments form conjugation tubes at the same time, giving the appearance of a ladder. Other common members of the Conjugales are Zygnema and Spirogyra.
Filaments sometimes produce short lateral, rhizoidal extensions, in a similar manner to the extensions which form the conjugation tube.
These may be in response to contact with a surface (the basal attachment has a similar rhizoidal appearance), but the branch so formed is always very short, and this is a rare occurrence.
Mougeotia isolates in culture:
Cultured in modified Bold’s Basal Medium (BBMPTB12 : Cox and Bold, 1966)
Mougeotia 8µm. (diameter ranges from about 5-8µm.) is the smallest species regularly found in low-pH waters. The following pictures are from cultures, and some of the characteristics are not regularly seen in field samples.
This is a typical view: the chloroplast in these cells is oriented parallel to the plane of view: the alga can change the orientation of the chloroplast to optimise its light gathering.
Another typical view: these cells are lying with the chloroplast normal to the plane of view. They can be clearly seen to have a pair of pyrenoids.
This picture shows an unusual arrangement of the chloroplast, which ought to be a single axial plate. This filament might be Entransia occuring as a contaminant of the culture, and would certainly be so identified in field material, but aberrant growth due to culture conditions cannot be ruled out.
Another atypical set of chloroplasts, appearing to wrap around the periphery of the cell. The cells in between, however, have the typical appearance of Mougeotia chloroplasts seen lying flat in the field of view. The last whole cell on the right has a pyrenoid clearly visible.
This is a degenerating filament of Mougeotia, with the cell contents gathered in a concentrated mass. This is a situation all too frequently found in some field samples, making them very difficult to identify.
Mougeotia 22µm.: This is one of the largest species regularly encountered in acidic waters, though larger do exist. The pyrenoids can just be distinguished in these cells.
Mougeotia 32µm, from Wester Ross. This sample, collected in August, was found to be undergoing lateral conjugation
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