It's a small nerite snail. We have two, the other is fine.
A few weeks ago I started finding it upside down on the gravel, like it had fallen from whatever it was suckered into. I turned it over as I read somewhere that they can't right themselves.
Then it stopped moving. Not moved for two weeks now. Occasionally a little bit of it's body comes out but then it seems to get stuck and when I look again it's fully sealed again.
I read that if they are sealed then they are alive. But this seems unwell at the least.
Is there much I can do? I have now taken it out of the main tank into another as I don't want it to pass anything on to the other snail/fish