Without a pic it'd be very difficult to identify a snail. There's just too many of them. Is it a really bright purple? If so check out pics of nudibranches.
I'd have to agree with incysor here, a pic is really needed for a positive ID. It could be a species of flatworm or a nudibranch, but without a pic to go by it's impossible to tell.
I too would have to agree with incysor and sugar magnolia. That's why my digital camera is my best friend, it's helped me through so many things so far. I recommend getting one, you could even get a real cheapy, or using a cell phone with camera function. Ya gotta love the technology Also if you find out what it is, be sure to let us know.