This review presents the scientific studies data on the special characteristics of developmental biology and epizo-
otiology of Cryptocotyle trematodes, which belong to Heterophyidae family and pose a threat to the health of the
endotherms, including humans, i.e., it is a typical zoonosis. These trematodes are predominantly widespread in
the Mediterranean region, namely, in the western Mediterranean region and the Aegean province. The trematodes
of Cryptocotyle genus are found in Europe, Asia, North and South America, and Antarctica. They are typical bio-
helminths, i.e., they have a complicated life cycle, where the initial intermediate hosts are mollusks, the second
ones – fish of different species, the definitive and final hosts are piscivorous birds, carnivorous animals (foxes,
wolves, dogs, cats, etc.), and humans. Cryptocotylosis is remarkable for its seasonal prevalence, which depends on
the climatic zoning of territories. For instance, in the territorial waters of Ukraine, the highest indices of crypto-
cotylosis invasion among Agonidae fish are mainly observed in summer and autumn, but the peak of the invasion
comes in autumn. The parasitizing of Cryptocotyle trematodes in the organism of mollusks impacts the reproduc-
tion ability and behavioral specificities (motility) of the latter. The invaded fish have black pigment spots on the
surface of their bodies – these are metacercariae. In the organism of definitive hosts, the agent is localized in the
gastrointestinal tract and may cause inflammatory processes in the mucous membrane of the intestines and changes
in parenchymatous organs, which demonstrates the toxic effect of the parasite on the host organism. The diagnos-
tics of cryptocotylosis is based on detecting the agent in the host organism and its further taxonomic identification
by its anatomic and morphological specificities. The pollution of the aqueous medium with organic and inorganic
residues impacts the organisms of both hosts and parasites.
