Final answer:
Pulmonate snails have adapted to life on land by transforming their mantle cavity into a respiratory chamber, which functions effectively as a lung.
Step-by-step explanation:
Snails that lack gills are indeed referred to as "pulmonate" and unlike their aquatic counterparts, they have adapted to terrestrial life. The mantle cavity in these snails is highly vascularized and has become a specialized respiratory structure, functioning effectively as a lung.
Therefore, their mantle cavity functions as a respiratory chamber, facilitating the exchange of gases with the surrounding air, rather than using gills like their aquatic relatives. This adaptation allows them to breathe air and survive in terrestrial environments.