Polymorphism and Ultrastructure of a Colpodean Ciliate of the Genus Platyophryides Foissner, 1987

A ciliate isolated from a pond in Brazil, transformed to a giant form when its food was shifted from a bacterial prey to a ciliate prey. This polymorphism is immediately reversible when the prey ciliates, either Tetrahymena or Colpidium, disappear from the culture medium. By its life cycle, morphology, and ultrastructure, this ciliate belongs to the Class Colpodea. it could belong to the genus Platyophryides Foissner, 1987, except that its micronucleus is not enveloped by the macronuclear membrane. The systematic position of the genus Platyophryides, the validity of the three species in this genus, and the characteristics of the Cyrtolophosidida are discussed.