Group portrait of Vorticella citrina (Muller 1786) a sessiline peritrich ciliate. Part of the Vorticella convallaria complex.This species is lemon yellow to light green in color. The body has typical inverted bell shape. There is a peristomal lip. Peristomal cilia wind counterclockwise to the cytostome. There are fine annular striations on the cell body. At the aboral pole is a scopula, the organelle that secretes the contractile stalk. The stalk is a contractile myonemes enclosed in by a sheath, which is ovoid in cross section. The stalk contracts in corkscrew fashion unlike the zigzag contraction of the stalk in the similar genus, Haplocaulus. The nucleus is short and horseshoe shaped. There is a single contractile vacuole. Vorticella is not colonial but may be gregarious. Primarily bactiverous. Collected from freshwater pond near Boise, Idaho October 2003. Brightfield optics.