Also found in: Dictionary, Medical, Wikipedia.
a subclass of protozoans of the class Infusoria. There are approximately 500 species of Suctoria. Suctorians may be sessile marine or freshwater forms. They are often stalked and are characterized by cytoplasmic and sometimes branching tentacles covered with a pellicle of slender elastic processes. There are numerous longitudinal microtubules in the axial part of the tentacles. Food is grasped, immobilized, and sucked up by the tentacles (hence the name of the subclass).
Some species of Suctoria parasitize the body of other infusiorians. In the adult state they lack a ciliated covering. The nuclear apparatus consists of a macronucleus and a micronucleus. Asexual reproduction is by means of external or internal budding. The segmented buds (zoospores) are ciliated and swim freely. They lose their ciliated covering upon fixing themselves to a substrate. Sexual reproduction is by conjugation, which occurs in a typically infusorian fashion in most suctorians; in some species the conjugants merge completely.