: Cyanobacteria (cyanophyta) are group of bacteria, previously known as blue-green algae. They are unicellular and non-motile, often coated with mucilagenous slime, and the photosynthetic membranes occur as thylakoids within the cell cytoplasm rather than being in a membrane-bounded chloroplast. The cyanobacteria have an extensive fossil record. The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old.