Cyanobacteria and amoeba. Polarised light micrograph of two spherical colonies of Nostoc sp. cyanobacteria (long, thin) and the empty shell of an Arcella sp. testate (shelled) amoeba (round). Cyanobacteria are bacteria that obtain their energy through photosynthesis. Arcella are found in freshwater ponds and puddles. They can develop vacuoles of carbon dioxide in their body to float up to the water's surface. Magnification: x100, when printed 10 centimetres wide.