In the old scheme of classification, i.e. the five kingdom scheme, Protista is a kingdom comprised of animal-like (protozoa), plant-like (algae), and fungus-like (slime molds and water molds) organisms. Accordingly, Protista is divided into several phyla. The plant-like or algal species are further divided into the following phyla: Euglenophyta, Chrysophyta (diatoms), Pyrrophyta (dinoflagellates), Chlorophyta (green algae), Phaeophyta (brown algae), and Rhodophyta (red algae).1 Recent studies and findings, though, would lead to changes in the taxonomic positions and to newer systems of classification.2 At present, Cyanophyta is now referred to as Cyanobacteria and is a phylum of bacteria. That is because this clade is comprised of species that are prokaryotic. In phycology, it is the only group of algal species that are prokaryotic. Thus, they are now classified as bacteria belonging to Phylym Cyanobacteria.
Cyanobacteria are found to be play a role in producing gaseous oxygen as a byproduct of photosynthesis. They are also believed to be associated with the Great Oxygenation Event.
Word origin: Greek (kyanós) = blue + bacteria
1 Pascher, A. (1914). "Über Flagellaten und Algen ". Berichte der deutsche botanischen Gesellschaft 32: 136–160. 2 The NCBI taxonomy database. Retrieved from .