I don't want to make fun of anyone but its interesting to see how we are all the same when it comes to strange creatures in our tanks. I remember thinking " what the hell happen to your shell" when I first saw a stomatella snail.
This is a great link for identification purposes, it always helps;
They can multiply quickly, but many fish/inverts may eat them. I love them, very cool and fun. A fun fact about them is, that they can "drop" their tail when picked at...the tail will wiggle and move to distract the predator while the snail gets away...very cool to see happen.