Final answer:
In gastropods, gaseous exchange is done through gills in aquatic species whereas terrestrial species use pulmonary sacs within their mantle cavity.
Step-by-step explanation:
Gaseous exchange in gastropods may involve different structures depending on whether they are aquatic or terrestrial. In aquatic gastropods, gaseous exchange primarily occurs through gills which are filamentous structures enclosed within the mantle cavity and are involved in exchanging gases with the surrounding water.
On the other hand, terrestrial gastropods do not have gills, instead, they use the lining of their mantle cavity as a respiratory organ that functions similarly to a lung, known as pulmonary sacs. This adaptation allows them to exchange gases with the air, which is a prime example of how gastropods have evolved to occupy various environmental niches.