* The references to most studies mentioned in the text are given in The Zoological Institute of the USSR Academy of Sciences, 150 Years (1982). The list of references given at the end of this paper includes the studies concerning theoretical aspects of biological diversity and the history of the collection of the ZIN only.

** A hapantotype is a preparation (slide) or a series of preparations containing the type specimens (direct relatives of each other) of the same protozoan species or a series of preparations of different developmental stages of the same species.