I have a planted tank with a few guppies in it and one fairly big snail. Don't know what kind of snail - I got him out of someone's planted tank because he was very cute and active. I did a partial water change this afternoon and a light vacuum of the gravel and noticed he was around then.....but now I noticed his shell is empty. I don't see him anywhere. Is he lurking around, and if so...with a new shell, or shell-less? I couldn't have vacuumed him out of his shell, could I?