Wow thank you for the fast replyIt's a ramshorn snail. They can be pests, and if you've got one, you've probably got at least a dozen more.
Personally, I like ramshorns. They can be pretty, and are good cleaners. They won't bother any plants, and don't cause problems. They CAN breed to extreme populations, but that's usually due to excess food. I never had mine grow past what my tank could handle, which was 3-4 in a 2.5 gallon.