Thanks everyone ........I found a thread that Dr Ron ID it
and it has a better pic pic than mine
http://reefcentral.com/forums/showth...ighlight=snail

and another good one
http://www.xtalworld.com/Aquarium/hitchfaq.htm

hitchhikers
 

Thanks Murry great hitchiker critter page with clear pics and some links
.....BTW I also have these snails and find them mostly on the glass and harmless