Differential interference contrast (DIC) light micrograph of Anabaena sp. algae. Anabaena is a genus of filamentous cyanobacteria and are known for nitrogen-fixing abilities. They are one of four genera of cyanobacteria that produce neurotoxins, which are harmful to local wildlife, as well as farm animals and pets. Anabaena is capable to differentiate specialized cells, the heterocysts (round dark green cells) and akinetes (oval large cell), to survive under different stress conditions. Under nitrogen limited condition, heterocysts provide the filament with nitrogen by fixing nitrogen. Akinetes are spore-like dormant cells that allow survival during adverse environmental conditions. Magnification: x475 when printed at 10 centimetres wide at its longest edge.