Walter,
That mystery snail of your looks like a fighting conch to me
No alarm however, fighting conches are much desired in most reef systems as they keep the sandbed clean of diatoms
Keep an eye on it and if it's out and about for a few days and then it disapears into the sand for another few days then I would say for sure fighting conch. You could also do a google search on fighting conch, that way you can compare pics as I don't have any images or I would post one.
I have three in my reef, which I had to pay $10 a piece for, so consider than a deal of a hitchhiker if it is a conch
Christy, I can't quite tell from the pic but I think yours is a snail and not a conch
