Metacercariae of Trematodes in the Snail Viviparus Contectus (Millet, 1813) From the Rybinsk Reservoir

Examination of 102 snails of Viviparus contectus from Rybinsk Reservoir in July–August 2023 revealed the presence of trematodes metacercariae of three families: Echinostomatidae, Cyathocotylidae and Leucochloridiomorphidae. Neoacanthoparyphium echinatoides was the species with the highest prevalence and intensity of infection (98.5%, 41.7, 1–192), followed by the Linstowiella viviparae (86%, 17.2, 3–45). Unencysted metacercariae Leucochloridiomorpha constantiae had a low prevalence and intensity of infection (13.7%, 0.51, 1–16). L. constantiae larvae parasitized only male snails. In contrast, the closely related species Leucochloridiomorpha lutea had high infestation rates (89.2%, 5.7, 1–20). L. lutea larvae equally infected of both the sexes of the snail. The sizes of cysts and metacercariae of all species are given. For metacercariae Neoacanthoparyphium echinatoides and Leucochloridiomorpha lutea, the infection intensity as a function of snail size was shown.