its nothing to worry about, my brother has a bunch in his tank, they dont really do much but theyre really good at proventing algae.. sorry. i dont really know the name
Without a better pic, I'd say it's a Stomatella snail. The shell on Stomatella snails is very small compared to their body size and looks more like a flat hat / cap than it does a shell. They are very common and most people end up with them without even trying to have them in their tank. They can easily come in on live rock and coral.
Looks like a stomatella to me too. I pic from its' top side would help. They breed like crazy but they just eat algae so it's a bonus, and they never get very big.