unknown snails ..... harmful ??

[OceanMist]

I got these snails in my aquarium that keep multiplying ... i can now count over 40 of them and they started with only 2 or 3, they are greyish white and have shells (although the shells are very small and flat, virtually unnoticable which makes them almost look like slugs) what are these things and are they harmful to anything? TIA

 

[Fluff]

Stomatella varia. Not harmful and great algae eaters.