Description of Acropisthium mutabile:
Medium-sized Haptorid ciliate, from 50-100 micrometres long. Body shape variable, from slenderly cylindrical to ovoid, or beet-shaped, with a pointed posterior. Oral aperture is apical, within a wide, bluntly conical snout. The base of the snout is encircled by a ring of long cilia. Body uniformly ciliated, with longitudinal kineties. Ciliation increased in density near the circumoral dikinetids. Clavate kineties forming dorsal brosse. Macronucleus spherical, contractile vacuole in the posterior. Freshwater, eats small algae.