Gloeotrichia cyanobacteria. Differential interference contrast micrograph of filamentous colonies of Gloeotrichia sp. cyanobacteria (formally known as blue-green algae). Each filament tapers from a basal, ball shaped heterocyst into a fine hair-like tip extending beyond the mucilage which holds the colony together. Magnification: x400 when printed at 10 centimetres wide.