infusorian.

With plural agreement. A class of Protozoa, comprising ciliated, tentaculate, and flagellate animalcula, essentially unicellular, free-swimming, or sedentary; so called because found in infusions of decaying animal or vegetable matter.Originally, as constituted by O.F. Müller, the Infusoria comprehended an assemblage of minute, usually microscopic, organisms, of many diverse kinds, including some now classed as vegetables, as the Diatomaceæ and the Desmidiaceæ. As now limited, the Infusoria are Protozoa characterized by a half-liquid endosarc, a firm cortical ectosarc, an outer membraneous cuticle, a mouth and anus, and a contractile vesicle which injects fluid. They were regarded by Huxley as a primary group in the animal kingdom.