40x

Please provide magnified image.

It looks like cyanophycean colony- Merismopedia

A cell is about 6 microns. The first image magnification is 200x (10x ocular and 20x objective) and the second, attached to my comment is 400x.

Dear Oana:

In my opinion the colony that you show in the picture it is not a Cyanobacteria. Merismopedia is a tabular colony as K. B. P. mentioned but I can see pyrenoid in the cells and there is neither choroplast nor pyrenoid in Cyanobacteria. Check if the cells are flagellated. The morphology of the colony is similar to that of genus Gonium. See the link below and observe your material searching by flagella. http://protist.i.hosei.ac.jp/pdb/images/Chlorophyta/Gonium/sp_2a.jpg

Good luck. Eugenia

I agree that the large colony appears to be Gonium, while the other small square cells appear to be a species of Cosmarium, a desmid. Good Luck.

I didn't see this kind of cells with flagella in that sample, but now I think that it looks like Gonium. I hope I will find it again in other samples for better observation. Thank you very much for helping me! Have a nice day! Oana

Donald and eugenia both are right.