my general rule when it comes to snails is if they randomly apper then you have a pest snail which will quickly multiply on you.
if you have to purchase them like a mystery snail or a netrate snail then you have a good snail that will be good for you aquruimus eco system.
what i would do now, is try to remove them as quickly as possible before they get out of hand, if youhave to clean any kind of surface you have as well for they will leave nests just about anywhere. my brother had these guys in his aquirum they left nests on his glass and plants and would drop down when hatched and emerge from the stones a few weeks later. look at the sticky above about pest snails.
i also want to note there are good snails out there, i have a few but these pest snails could put people off from owning any snail.
good luck