Picture isn't super clear but that appears to be a vermetid snail, try googling that and see if it looks like the photos that come up. If it does then take some superglue and put a decent dab on the end of the tube. They aren't particularly welcome in reefs because the mucus net they use to feed has been known irritate corals. that and tubes can be quite shape and fairly easy to cut yourself on when working around the tank.