Snails (Gastropoda) are molluscs with one shell. They are one of the most recognizable groups of organisms. Although most have the helical or spiral shell, one family, Ancylidae, has a flat conical shell. So "one shell" rather than helical shape is the key feature of snails.
There are 9 families of snails containing 22 genera and at least 28 species in Ohio.
They range in tolerance to pollution from facultative to somewhat tolerant.