Several more of these snails are crawling around the tank. They are quick little buggers for their size. Reading about them and it seems to be a mixed opinion of leaving them in or trying to get rid of 'em.
It really depends on the hobbyist I suppose. I personally dont mind them as long as its a suitable number. But if they get out of control then theres a problem. Mostl likely they are pond snails. Hitchhikers that came in with your plants. Depending on the amount you have in there for a 5gallon tank it may prove to be too much. But then again most people assume theyll devour your plants but I have yet to experience this(knock on wood)