I've been looking into those Vermetid Snails - I think it might well be then, despite never having seen anything that remotely resembles a head. I went to that Coral House (the base of mailordercorals.com) yesterday for some shrimp and showed your man Gary the picture. He immediately thought it was those snails without hesitation and the more I read about them the less I want him to be correct! I suspect he is though, because I have seen a couple of pictures of things that look like them. I'm also pretty sure there are juvenile snails kicking about (which the juvenile vermetid's do) so I may already be fighting my first pest war as a result of the first bit of coral I have put in my tank. On the plus side the Fire Shrimp I got from Gary look great and have drawn the original one from hiding to boot!