Portrait (ventrolateral view) of the microthoracid ciliate Pseudomicrothorax dubius (Maupas, 1883) Penard, 1922.The cell outline is oval with right edge more curved than left edge. Laterally compressed. The right and left sides of the inflexible pellicle have curved longitudinal ciliated grooves separated by broader flat ridges. Somatic ciliature restricted to 13-14 longitudinal kineties more on the right than the left surface. The oral aperture is in anterior 1/3 of body in a shallow depression. The cytopharynx is supported by fine transverse trichites. There are 3 short membranelles on the left of the cytostome and a short undulating membrane on its right. There is a small group of unciliated basal bodies posterior to the undulating membrane. This is a primordial stomatogenic field. There are many fusiform peripheral extrusomes. Macronucleus elongate ovoid, centrally placed with single micronucleus. The contractile vacuole is centrally located. P. dubius feeds on cyanobacteria giving it a green to green-blue color. Collected from a freshwater stream near Boise, Idaho. DIC.