Phacus is a genus of unicellular protists, of the phylum Euglenozoa (also known as Euglenophyta). They are light-green and are commonly found in freshwater pools, propelling themselves by gyrating their bodies. They have a single flagellum which is often as long as the Phacus' body. Euglenid, with plastids, rigid, flattened cells, most species very flat and leaf-shaped, often with ridges, folds or grooves running helically or longitudinally, giving an irregular or triradiate cross-section; many species with a long posterior spine, many twisted, flagella, eyespot and flagellar swelling as in Euglena; chloroplasts usually small, discoid, numerous, without pyrenoids; a few species (e.g. P. splendens) have large flat chloroplasts with pyrenoids; paramylon is typically deposited as a few large