Veterinary parasitologists: the time has come to talk about the use of the expressions "Protozoan" and "Protista".

Abstract

The classification of eukaryotic organisms has evolved significantly over the past years. For a long time, the five-kingdom model proposed in 1969, which included the kingdoms Monera, Protista, Fungi, Plantae, and Animalia, dominated biological classification. However, recent advances in molecular biology, particularly phylogenomic studies, have challenged this classification as it does not accurately represent the evolutionary patterns of a vast diversity of organisms, especially those formerly known as protozoa. Currently, Protista is no longer considered a valid taxon, as the organisms previously classified in this group are highly divergent and not monophyletic. Modern approaches now classify eukaryotes into several supergroups, with "protozoa" now dispersed among different groups. For example, parasites once grouped as "protozoa," such as Babesia (Apicomplexa), Trypanosoma (Euglenozoa), and Entamoeba (Evosea), are now placed into distant branches of the tree of life and within different supergroups. Although this supergroup classification may change in the coming years, it provides a more accurate representation of evolutionary relationships among eukaryotes. However, this issue has not been adequately discussed by the veterinary parasitology community. This article advocates revisiting these terms in light of modern classification systems to ensure a more accurate and biologically realistic terminology that reflects current knowledge.