Definitely a leech. They often come in on plants. The ones in my tank were harmless. Didn't hurt fish, snails or shrimp as far as I could tell. I even caught some and left them in a jar with some snails to see if they would eat them, but they didn't.
Once in a tank they can be hard to eradicate. You can make a trap out of a plastic drink bottle. Cut the top off and stick the cut off part back into the bottle upside down. Put some bait in and put the trap open side down on your substrate.
I used to feed them to my Pearl Gouramis and rams who were in a different tank, so some fish do eat them. It's possible that something like rams would clean them out of the tank.
Life isn't stone, it's water.
PSA: When talking about baby fish, "fry" is plural.
I have a fry. I have some fry.