Green algae - Ankistrodesmus and Catena
The picture shows Ankistrodesmus (in the centre) surrounded by a lot of small cells of the genus Catena. Catena has very small cells (2-5 my) often two and two held together with a brown thickening in the ends.
The size is about 2-5 my (1my=1/1000mm). The picture shows Ankistrodesmus in higher magnification. The colony is made of long pointed, slightly curved cells. The length is 60 my.