Seventy-four specimens from four genera of native gastropods were cooled from 2.0°C to — 3.3°C over a 3 hour period under laboratory conditions. The taxa examined included two terrestrial pulmonates {Anguispira alternata and Mesodon inflecta), a pulmonale known to occupy both permanent and ephemeral aquatic habitats {Physella mtegra), and an aquatic prosobranch {Pleurocera canaliculatum) . There was no mortality in the pulmonates, but 39% mortality occurred in the prosobranch Pleurocera. Additionally, a sample of 43 zebra mussels {Dreissena polymorpha), a non-native but recently introduced species, were aerially exposed to the same temperature cycle. Of the 43 mussels, 20 had been acclimated to 2°C, and 23 acclimated to 15°C. Mortality occurred in both treatments (35% mortality in the 15°C acclimated and 25% in the 2°C acclimated) and did not differ significantly between the two groups. No mortality occurred among controls.