Phenotypic variation in radulae has been studied in several littorinid species because of this organ's intrinsic relationship with diet and, consequently, with the environment. In this work, we compared the radulae of the Brazilian species Littoraria flava found in mangroves and on rocky shores. Individuals of L. flava showed marked differences in the shape of the cusps among samples from rocky shore and mangrove. In a transfer experiment, the shape of the radula changed within 40 days. A different response was observed in individuals transferred to mangrove, where two different phenotypes were found, suggesting either intrapopulational variation in the responses to change of environmental conditions, or that some snails showed a slow reaction to the environmental changes. The alterations could be attributed to ecophenotypic plasticity. Analysis of variance showed that the length of the radula in L. flava was strongly influenced by the substrate (F6,22 = 17.13, P < 0.000), but apparently not by the transfer experiment. © The Author 2005. 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