Microcystis Lemmermann

From Greek mikros, "small" + kystis, "bladder"
 
The cells of Microcystis are small - only a few microns in diameter - and lack individual mucilage sheaths. The cells are usually arranged in colonies that are initially spherical but become irregular or perforated over time. The cells may be grouped tightly or sparsely within the fine, colorless colonial mucilage. The colonies are free-floating and may
be composed of clustered subcolonies. Smaller colonies are microscopic, while larger colonies
may be viewed with the naked eye.
The cells are spherical or hemispherical after dividing. The protoplast is a pale blue-green, but overall the cells appear dark or brownish due to the presence of
gas vesicles. This feature easily distinguishes Microcystis from Aphanocapsa
under light microscopy.
In culture, cells may exist singly or in irregular clumps.