Phacus Dujardin
From Greek phakos, "lentil"
The euglenoid Phacus has oval-shaped or spherical cells that
are often flattened and leaf-like. Some species may be
twisted throughout the cell (Phacus helikoides) or only at the
cell posterior (Phacus tortus). The pellicle is quite rigid and is composed of wide proteinaceous strips that prevent the elastic metaboly movements seen in Euglena and other euglenoids.
The cells instead move by gliding and swimming with their single emergent flagellum. The chloroplasts may be small and spherical without pyrenoids, or large and discoidal with pyrenoids present.
The cytoplasm of euglenoids contains many paramylon starch storage granules, which are usually
donut-shaped in Phacus cells. Like other freshwater euglenoids, Phacus cells have contractile
vacuoles and may have a red-pigmented stigma to sense light.
In the images below, note the cellular morphology, organelles, and the pellicle covering the cell.