Classification: Taxonomic ranks under review (cf. Illustrated Guide to Protozoa, 2000. Allen Press)
Protista (unicellular eukaryotes)
Apicomplexa (cells with cluster of organelles known as apical complex)
Coccidea (gamonts small and intracellular, form small resistant spores called oocysts)
Eimeriida (gametes develop independently without syzygy; known as coccidian parasites)