This work is devoted to the analysis of the influence of trematodes on the organism of the mollusk host and its symbionts. We used metabolomics methods to investigate how infection affects the biochemical processes in host tissues. To analyse changes in the microbiome as a result of parasitic infestation, we also performed 16S rDNA sequencing of microorganisms from the guts of these mollusks. We collected two species of mollusks (Littorina saxatilis Olivi, 1792 and Littorina obtusata Linnaeus, 1758) from the coasts of the Barents Sea. Mollusks of both species, infected with Microphallus pygmaeus (Levinsen, 1881) and uninfected, were collected from two levels of the intertidal zone (upper shore level and lower shore level) of the Varanger Fjord (N 70.040, E 29.584) then their tissues (without parasites) were analysed by GS-MS methods. To analyse the microbiome of mollusks, samples of bacteria from the intestines of snails of two species, infected with Microphallus pygmaeus trematodes and uninfected, were collected in Dalnye Zelentsy (N 69.117, E 36.070) then 16S rDNA of the microorganisms was sequenced using Illumina MiSeq sequencing. Additional information may be found in the mentioned paper.