Here's why:
* Saltwater is toxic to freshwater snails. Their bodies are adapted to freshwater environments and cannot handle the high salt concentration in saltwater.
* Osmoregulation: Freshwater snails maintain a balance of water and salts within their bodies through a process called osmoregulation. This process is different in saltwater animals, and freshwater snails cannot adapt to the osmotic pressure changes in a saltwater environment.
* Physiological differences: Freshwater and saltwater snails have different physiological adaptations, such as the structure of their gills and the way they regulate their internal salt levels.
Trying to put a freshwater snail in a saltwater aquarium would be fatal.