High Quality Content by WIKIPEDIA articles! Vorticella convallaria is a protozoan. It forms part of the V. convallaria species complex. V. citrina is lemon yellow to light green in colour.Protozoa (from the Greek words proton, meaning "first", and zoa, meaning "animals") is a subkingdom of microorganisms that are generally classified as unicellular non-fungal eukaryotes. Protozoans play a key role in maintaining the balance of the ecosystem.