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We used multiple analytical methods to demonstrate resource partitioning in five species of coexisting endemic gastropods in the family Baicaliidae and the genus Megalovalvata (Valvatidae) in rocky walls of the underwater canyons in Lake Baikal. We tested whether filter-feeding baicaliids and valvatids consume and assimilate different food using data from gut contents, stable d 13 C and d 15 N isotopes and radular morphology, with subsequent combined analyses. Our results showed that the four baicaliid species assimilate microalgae, diatoms and bacteria, whereas the single Megalovalvata species mostly assimilates plant detritus. The d 15 N variations in the baicaliids reflect differences in their digestion of seston components, whereas the d 13 C similarity illustrates consumption of food particles derived from similar primary producers. Gut contents in the baicaliids were dominated by a single species of planktonic diatom, although more than 30 species of microalgae were recorded in all seasons. However, the composition and quantity of additional food particles varied by species. Our results showed that baicaliids have significant fine scale differences in radular tooth morphology, which may allow partitioning of food resources.