The species composition, ecological distribution, and trematode invasion of mollusks of the genus Littorina were studied in four localities of the eastern Murman coast. Six littorinid species were found: Littorina saxatilis (Olivi 1972), L. compressa Jeffreys 1865, L. arcana Hannaford Ellis 1978, L. littorea (Linnaeus 1758), L. obtusata (Linnaeus 1758), and L. fabalis (W. Turton 1825). The first three species belong to the "saxatilis" group, the rest ones, to the "obtusata" group. The conchological characteristics given in the article can be used to refer a mollusk to one of the species complex - "obtusata" or "saxatilis". Species identification within each complex is possible when using such anatomical features as morphology of penis (for males) or palliai oviduct (for females). The more detailed characters are the length of penial filament, number and size of penial glands, size of copulative bursa, and the correlation between the length of the bursa and that of jelly gland. The analysis of the vertical zonation of littorinid species showed that L. compressa, L. obtusata, and L. fabalis inhabited the fucoid zone (populations of the latter species occupy the lower intertidal zone). L. arcana occurred on stones in the upper intertidal zone. L. saxatilis populations were found in a wide range of intertidal areas. The parasitological analysis of littorinids has revealed 12 trematode species. The data obtained cannot be used for the determination of differences between "saxatilis" and "obtusata" species complexes (or between the distinct littorinid species). The results are compared with the previously obtained materials about littorinids inhabiting the White Sea.