Cell wall flexible, from slight flexing to substantial changing of shape, due to proteinaceous strips of wall material (known as a pellicle). Cells rounded to spindle shaped. Flagellum single (sometimes absent), emerging from a pit at the cell apex known as a reservoir. Obvious red eyespot near reservoir. There may be many round chloroplasts per cell and numerous paramylon granules. Deal cells become round and motionless, but can often still be recognised by their dense green colour and bright eyespot