Percolomonas cosmopolitus (Ruinen, 1938) Larsen and Patterson, 1990. Obovate cell, 6-10microns long, with a ventral groove arising subapically and extending half the length of the cell. Four flagella insert subapically: one approximately twice the length of the cell, extending behind the cell, used for adhesion to substratum: three shorter flagella lie within the groove and are used to creat a current of water from which suspended particles are extracted. Nucleus anterior, with globular nucleolus.