Hi, James and all- Yes, there are mollusks in Ohio, fresh water ones.
Many years ago, when the Pittsburgh Shell Club was very active, we
went on a wonderful shelling trip to the Walhonding River (definitely
in Ohio) - there were both bivalves and univalves to be found.
The Club shell was called Lymnia Stagnalis ( a fresh water species
I believe and I don't know if it is found in Ohio but it could be)
I'm no expert on fresh water shells.
Karen VV