Radular structure and grazing effects of six snail species were examined to determine if differences in radular morphology might be related to resource partitioning through the selective removal of attached algae. Nutrient-releasing clay pots were incubated inside grazer exclosures in Douglas Lake, Michigan, for 25 days to generate a uniform growth of attached algae. The pots were collected, gently rinsed of loose material, and placed in laboratory aquaria. Five individuals of each snail (Physella gyrina, P. parkerii, Lymnaea emarginata, L. stagnalis, Helisoma anceps, and Elimia livescens) were each allowed to graze on a separate piece of clay pot. Algae on grazed and ungrazed substrata were examined using SEM and light microscopy. All snails visibly reduced algal density, leaving clearly defined grazing trails. The prosobranch Elimia livescens was significantly less effective (p < 0.05) than all pulmonates in removing attached algae. There were no significant differences among pulmonate species in grazing effect. The results indicate that variations in radular structure may be relatively more important in determining different grazing capabilitiies between prosobranchs and pulmonates, rather than between closely related species of the latter. If food resources are limiting to snails in this system, factors other than selective ingestion, e.g., behavioral differences, may also be operating to reduce competition.