ok if you search under my name as the author and on the second page it says found something weird.I highlightened a bit and paste below.
Sounds to me like a Vermetid snail. If it is there harmless and a good sign that your tank is healthy. Here's an article by Shimek, scroll down to about the middle of the page... http://www.reefkeeping.com/issues/2005-01/rs/
There is a link to read on it but its definately vermetid snails it says.
cheers
george