Cyclonexis erinus a rare organism?

Cyclonexis erinus (Chrysophytes, golden algae) is considered to be an algae, difficult to observe. The specimen shown in this video has been found in an aquatic sample taken from a small fen in the Nature Reserve ‘De Teut’ in Belgium, in February 2016 (during quite cold weather).

Only few references about this algae can be found in literature and on the internet. Only a very limited number of the species Cyclonexis sp. is known. Cyclonexis sp. lives in cool, lime poor mountain waters and in acid fens containing Sphagnum. It is mentioned that it is not so rare as is sometimes assumed. It was discovered that these algae disintegrate very quickly when external conditions are changing, causing it to disappear from the aquatic sample.

The disintegration of the cells of Cyclonexis sp. is caused by the so-called ‘discobolocysts’, small explosive organelles that can swell and explode with a change in external conditions, whereby a small thickened piece of the cell wall (the discus, diameter 2 microns) is launched. Usually the cell is immediately destroyed and because it has no strengthened outer wall, it looks as if the cell suddenly dissolves in the water.

This is the reason why this type of algae is difficult to observe, because disintegration takes place under the microscope when the temperature of the sample rises from ≥10 oC to room temperature. However, it is most likely that if one goes searching for these algae in suitable waters and investigates the aquatic sample immediately, that this interesting organism can be found on more places.
The algae shown in the video on the right hand side of Cyclonexis erinus is a common Desmid: Micrasterias truncata sp.

Source: W.F. Prud’homme van Reine, Governmental Herbarium Leiden, The Netherlands
With thanks to: J. van de Sande, Dutch Society For Microscopy