my swimming snail

strangest thing i've ever seen. he was one of those hitchhikers that stows away
on plants you get at the LFS. he kinda hung around and hasn't multiplied
(strangely enough). he's about the size of a nickel now (slightly less than 2
cm.) with a shell that spirals around upon itself, not coiled to one side or the
other. he'll make his way to the top of the tank then just... let go. he'll free
float for a while in mid water then swims (actually i'm sure he just drifts)
toward something he can grab onto and then goes again. occasionally he gets real
ambitious and climbs up the side, lets go, floats for a minute or to, then drops
like a rock to the bottom, races to the other side of the tank and does it all
over again.

anybody else have one of these?