Polyclad Leopard Flatworm
Pericelis byerleyana which gets up to ~2.75"/7cm and (probably) eats snails. You might be able to get away with offering frozen snail meat (surprisingly readily available online) if you really want to keep it without offering it live snails - no guarantees it would take frozen meat or derive the nutrition it needs from any of the frozen snails available on the market though.
Edit: Knew I remembered something about these guys feeding on things beside snails - Exnisstech had one (closely related
Pericelis tectivorum) that ate clam meat, which may be a good option too:
Had a clam on the half shell hanging in my stock tank working on getting my new CBB to eat food offerings. Came back and this big ol flat worm was on the clam. I pulled it and put it in a container. This is the stock tank All of the rock came out of my 180g that I recently broke down. Might...
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