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.