Pleurostomum flabellatum Ruinen, 1938. Cell 11-14 microns long, spindle-shaped and round in transverse section with two parallel flagella inserting apically. The flagella are 0.5-1.5 times body length. They are often, but not always, the same length. The flagella were usually observed stuck to the coverslip or slide. When free the flagella beat homodynamically. Subapically there is a wide and deep opening or groove that runs half to three quarters the way down the body in a half spiral and usually ends in close association with a food vacuole. The body was not observed to bend or flex except in one individual where the posterior third of the cell was stuck to the coverslip.