Whats this invert?

[Nyghtfire]

Looking in my tank this morning I found what looks like a snail walking for lack of a better term across a larger snail. Thing that's throwing me is it's shell and skin are different any idea what it is? Cheers.

 

[slitherbomb]

It looks like a limpet.

 

[mr_X]

stomatella snail. harmless herbivore.