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a subclass of protozoans of class Infusoria.
The body in Peritricha is bell-shaped. A broad oral disk bears spiral rows of cilia. Feeding is phagotrophic. Reproduction is by longitudinal fission. There are two orders, comprising more than 1,000 species. The majority are sessile (order Sessilida), either solitary (for example, Vorticella) or colonial (Zoothamnium); they attach themselves to the substrate by means of a basal disk, pedicel, or shell. A ciliate ring serves for locomotion in the motile forms (in the sessile forms it appears temporarily in the motile embryos, or zoospores). Motile Peritricha (order Mobilida) use a broad ring of grasping hooks for temporary attachment to a substrate. Peritricha inhabit both fresh waters and marine. The sessile forms live on any firm substrate, including aquatic plants and animals. The motile forms live only on animals (from coelenterates to amphibians) or their viscera. During periods of massive reproduction, Trichodina and representatives of closely related genera do damage to the integuments of their animal hosts (especially of fish fry), causing possible illness or death.
A. V. IANKOVSKII