Green algae - Crucigeniella
Crucigeniella has many four-celled colonies joined together to make big flakes in special order.
The length of the cell is about 10 my. The brown colour in the picture is due to the fix -liquid. The cell has a cell body called pyrenoid side by side with the chloroplasts. The pyrenoid has a meaning in the starch production. Crucigeniella is common in polluted water.