Corliss, John O. Department of Zoology, University of Maryland, College Park, Maryland.
Last reviewed:August 2019
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A specialized subclass of the class Ciliatea composed of a large group of unusual-looking ciliate protozoa. It has excited the curiosity of microscopists for nearly 300 years. Many are sessile and stalked, while some form colonies which may reach a large size. A number are attached as ectocommensals to a variety of animals and plants. A free-swimming stage in the life cycle, indispensable for distribution, is known as the telotroch. It is a small, mouthless form equipped with a single girdle of posteriorly located locomotor cilia. This is quite unlike the morphology of the mature, sedentary form, which is an inverted bell form atop a long stalk. The body is naked of ciliature except for conspicuous wreaths of buccal ciliary organelles at the oral end. Much is made by many protozoologists of the fact that the adoral zone of membranelles, in this instance, winds counterclockwise toward the mouth. Actually, this may be of little real importance, although convenient in taxonomic keys. Vorticella (illus.a) and Epistylis are probably the best-known stalked forms. The former is a solitary ciliate, the latter a colony builder. Trichodina (illus.b) belongs to the group of mobile peritrichs. Its species are associated with a wide variety of invertebrate and vertebrate hosts on which its actions range from those of a harmless commensal to a pathogenic parasite. The subclass Peritrichia contains a single order, the Peritrichida, whose species may have evolved from such holotrichian orders as the Hymenostomatida or the Thigmotrichida. See also: Ciliatea; Ciliophora; Hymenostomatida; Protozoa
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