Final answer:
Aquatic mollusks breathe using gills which allow for gas exchange with the surrounding water, unlike terrestrial mollusks that use the mantle cavity for gas exchange.
Step-by-step explanation:
Aquatic mollusks breathe using gills, which are thin filaments that absorb gases and exchange them with the blood and surrounding water. Terrestrial mollusks, in contrast, exchange gases with the air across the lining of the mantle cavity. However, for the specific question asked, aquatic mollusks utilize gills to respirate in their underwater environments.