A distinct external shell abnormality, coarse seam, was found in a high percentage of the pond snail Lymnaea stagnalis (L.) collected near Chernobyl Nuclear Power Plant (NPP), Ukraine. The negative cytogenetical and hematological effects of long-term irradiation on pond snails in the Chernobyl Exclusion Zone have been repeatedly reported; consequently, it has been assumed that radioactivity may also affect shell morphology. However, due to the absence of this shell abnormality in pond snails collected from two radioactive sites in Russia, it can be concluded that the appearance of abnormal shells in snail population near Chernobyl NPP cannot directly be explained by the radioactive contamination.