protozoan classification used to be based on their means of
Protozoa Historically, the Protozoa were classified as "unicellular animals", as distinct from the Protophyta, single-celled photosynthetic organisms (algae) which were considered primitive plants. Both groups were commonly given the rank of phylum, under the kingdom Protista.[45] In older systems of classification, the phylum Protozoa was commonly divided into several sub-groups, reflecting the means of locomotion:[46] Classification schemes differed, but throughout much of the 20th century the major groups of Protozoa included: