Today when I went to feed my p's, I noticed a small round dot on one of my plants. At first, I thought that it was just a whole in the plant. But as I looked, it started to move. I've had my tank and my p's for a little over 3 weeks and never once saw a snail. Should I be worried? Or is this normal? I've read that they can be a menace as they breed like crazy and are hermaphrodites. Could they cause any harm to my p's and if so, how do I eliminate them?
Here's a pic

Here's a pic