Blue-green bacteria - Anabaena flos-aquae
Aanabaena flos-aquae are twisted. Large number of filaments can form loose tangles.
Probably this is one of the most widespread species in the Northern countries. Occurs in all kind of water, but mostly in water rich in nutrients (eutrofic water).
The cell has diameter of 4-10my.
Among the ordinary (vegetative) cells you can observe two types of quite different cells that are bigger and have a different form compared to the ordinary cells. The greatest ones are heterocysts, which are known for utilisation of atmospheric nitrogen as a nutrient. The process, called nitrogen-fixation, gives the Anabaena a nutritional advantage over other algae in an environment. The resting spores are the other type of special cells.
The image shows resting spores as the largest cells you observe on the filament, down to the left. Above the resting spores is a heterocyst. The other cells are ordinary vegetative cells.