What evidence would indicate whether this animal is aquatic or terrestrial in mollusca?

When there is the presence of gills it will be easy to determine if the animal is aquatic or mollusk.

Aquatic means related to water. While Mollusca is termed as the large phylum of invertebrate animals whose members are called mollusks. Most of the mollusks live in water.

The most numerous mollusks are mantle which is important for cavity and is used for excretion and breathing, the presence of radula and their structure of the nervous system.