ON THE CONCEPT OF KINGDOMS, WITH SPECIAL REFERENCE TO THE ANIMAL KINGDOM

Many data - molecular as well as cytological and cytochemical - have r ecently been accumulated for a wide variety of organisms, resulting in profound changes in our conceptions of the phylogeny of the living wo rld. At the taxonomic level, the apposition of two kingdoms - animal a nd plant - is no longer acceptable, since all living species are likel y to be distributed between three, very early-differentiated, major li neages, one of which (eukaryotes) includes all species conventionally classified as animals. However, within eukaryotes, some unambiguously monophyletic groups include both ''animals'' and ''fungi''. One of the se groups, for example, is made up of two subgroups, one comprising th e ''true fungi'' (eumycetes) and the other divided into two sister tax a, the choanoflagellates and Metazoa. The term ''animal kingdom'' migh t be used to refer to either Metazoa only, or to the group including M etazoa and choanoflagellates. In this situation, a consistent classifi cation of eukaryotes would have to include dozens of kingdoms and many other taxa of even higher rank On the other hand, an assemblage inclu ding all photosynthetic eukaryotes would be polyphyletic. Thus, it is suggested that the word kingdom should be dropped from the modern scie ntific vocabulary.