Detail of oral infraciliature of the hymenostome ciliate, Pleuronema coronatum (Kent, 1881). The cell is ovoid to fusiform and slightly dorsoventrally compressed. The teardrop shaped peristome begins subapically and extends about 2/3 the cell length. There is a prominent undulating membrane on its right border. This curves around the posterior margin of the peristome forming a distinct pocket. The cytostome is in the depths of this pocket. Fibrils radiate from the margin of this pocket to the cytostome. There are three adoral membranelles. M1 begins at the anterior end of the undulating membrane and forms an acute angle with it as it extends posteriorly for a short distance. M2 is bipartite. The long anterior portion begins in the angle between M1 and the undulating membrane and extends posteriorly to the termination of the undulating membrane. At the posterior end of this part there is a sharp indentation rightward toward the peristome. This feature of M2 differentiates the "coronatum"ï¿½ type oral apparatus from the "marinum" type in this genus. There is a separate V-shaped part of M2 on the right side of the peristomal pocket. Some workers describe this as M3 but Foissner includes it as part of M2 and designates the two divergent kineties to its left as M3 (Foissner W., Berger H and Kohmann F. Taxonomische und Ã¶kologische Revision der Ciliaten des Saprobiensystems- Band III: Hymenostomata, Prostomatida, Nassulida. Informationsberichte Bayer. Landesamtes fÃ¼r Wasserwirtschaft. 1/94: 278-284, 1994). There are approximate 35 somatic kineties with 2 to 6 preoral kineties and no postoral kineties. There is a short preoral suture and a broad postoral suture in the center of which the cytopyge is located. The anterior apex of the cell is unciliated. There are many longer caudal cilia. The otherwise very similar P. crassum has no tuft of longer caudal cilia. The spherical macronucleus is central and has 1 to 8 adjacent micronuclei. The single posterior contractile vacuole empties through a dorsal excretory pore. Stained by the silver carbonate technic (see Foissner, W. Europ. J. Protistol., 27:313-330;1991). Collected from a freshwater pond near Boise, Idaho March 2005.