Snails are great against dissolving diatoms & detritus (small particles of food). These small fellows suit best for the Beginner level aquarist. The name snail applies to most members of the molluscan class Gastropoda that have coiled shells. Other gastropods, which lack a conspicuous shell, are commonly called slugs, and are scattered throughout groups that primarily include snails. Snails are found in freshwater, marine, and terrestrial environments.