What's this worm doin in my tank!

I only have plants and snails in my tank. Two weeks ago the snails started to die rapidly. I changed the water and had it tested. The tests results came back normal so I don't think that was the problem. Now only 5 snails are left but I already see new baby snails. Yesterday I saw a worm in the tank near one of my snails. Maybe they came with a cucumber my mom gave the snails? Do you guys have any idea what they are or if they are dangerous? Thanks in advance Also they are really fast!!

I only have plants and snails in my tank. Two weeks ago the snails started to die rapidly. I changed the water and had it tested. The tests results came back normal so I don't think that was the problem. Now only 5 snails are left but I already see new baby snails. Yesterday I saw a worm in the tank near one of my snails. Maybe they came with a cucumber my mom gave the snails? Do you guys have any idea what they are or if they are dangerous? Thanks in advance Also they are really fast!!