Snail identification

[abreefer]

I have an unknown snail in my reef tank. It has a standard snail body (like a Nassarious, but without the breathing tube.) It is about 3/4 inch long, and gray. The shell looks like an afterthought. It is hemispherical, and only about 1/4 inch long. It looks like a little half round cap. Any ideas??

 

[fishfreek]

Does it look like this?

If so then its totally harmless.

http://www.reefs.org/hhfaq/pages/main_pages/faq_rock2.htm

Click on the above link for some more info on them. Look toward the bottom of the page.

 

[abreefer]

I would say that is it. Thanks.
Bob