have used the term as a synonym for Ciliophora. In modern, formal classifications, the term is considered obsolete; the microorganisms previously and colloquially referred to as Infusoria are mostly assigned to the clades Diaphoretickes (e.g. ciliates, most algae), Amorphea (e.g. crustaceans and other small animals) and Discoba (euglenids).

In other contexts, the term is used to define various