These Apple snails, sometimes called Mystery snails, are quite popular in FW setups. They are interesting and attractive creatures. They have a snorkel tube that that they can extend an inch or more so they can breathe air from surface (they have a lung) without having to expose themselves on surface. They can also float upside down and form part of their 'foot' into a cone which they use to suck down food particles like flake floating on surface. Unlike most snails they won't eat live plants. They are sexual i.e. there are males and females unlike most snails which are hermaphrodites. They lay clutches of eggs just above the water level so unlike other FW snails you can keep the numbers under control. I let mine breed like rabbits and sell the offspring to an LFS--the proceeds pay for practically all my fishfood. And on top of all that, they are good to eat!!
Applesnail.net has all the info about them, and recipes too!!