Well, I have to edit my post here... I had one of the little guys you have in your palm, the brown w/ gold spots... I now have identified the 1/2" snail it grew into as a brown ramshorn. That's not to say it's the same one I originally saw; this one could have been hiding somewhere but I think I would have seen him. I moved a chunk of driftwood and found a smaller dead ramshorn, which I think starved when I had no fish and was not feeding the tank for a couple of weeks, and this guy ate him and grew fast...
In short, I bet the little guy you have grows into this: