The spathidiids belong to the ciliate subclass Haptoria (Protozoa, Ciliophora), that is, they are predators using toxicysts to overwhelm the prey. Spathidiid ciliates prefer terrestrial and semisterrestrial habitats, but many occur also in freshwater, and some are marine.

Over 200 nominal spathidiid species have been described, sometimes based on seemingly minute differences. Thus, many protozoologists considered them as indeterminable and claimed for a detailed revision. The present monograph carefully revises the taxonomy, nomenclature, and ecology of all nominal species...