Light micrograph of the freshwater blue-green alga (cyanobacterium) Anabena spec. Anabena forms unbranched, mostly blue-green to brown unicellular filaments with spherical cells, as in all cyanobacteria without nucleus and plastids. In the filaments there are some thick-walled, colourless heterocysts and large, oval acinetes. Culture material of the algae collection at the University of Cologne (CCAC). Microscopic contrast method : Differential interference contrast. Magnification 600x at a print width of 10 cm.