Peritrichia

(invertebrate zoology) A specialized subclass of the class Ciliatea comprising both sessile and mobile forms.

A specialized subclass of the class Ciliatea composed of a large group of unusual-looking ciliate protozoans. Many are sessile and stalked, while some form colonies which may reach a large size. A number are attached as ecto-commensals 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.

Vorticella (illustration a) and Epistylis are probably the best-known stalked forms. The former is a solitary ciliate, the latter a colony builder. Trichodina (illustration b) belongs to the group of mobile peritrichs. See also Ciliatea; Hymenostomatida.

Peritrichida. (a) Vorticella, a stalked peritrich, (b) a mobile peritrich.