Nelveeta Lytle, age 15, of Winston Salem, N.C., for her question:

WHY ARE SNAILS PUT INTO AQUARIUMS?

Snails found in aquariums are the type you also find inponds. They are very helpful because they eat the minute green plants that would otherwise form a film on the glass. They are very much like tiny vacuum cleaners and are used to keep aquariums clean.

Limy shells cover the snails and you'll notice they form into spiral coils. In some snails the coil twists to the left and in others to the right. Both the left and right coils may be found among snails of the same species.

Relatives of the aquarium snails are eaten by many people. Called the periwinkle, the small edible snails are popular in Europe and along the Atlantic Coast of North America.