black snail thing

[asherah]

I was looking in my today and I noticed this little oval shaped black snail thing crawling around my corals. What the heck !
It looks like some sort of slug but with a shell ...but it's kind of a flat shell.. maybe it's not a shell ? =p Whatever it was it has 2 antenae as well.
Also the bottom of it is white.
I tried to get a picture but my camera won't focus in very well. It's only about 1/2 inch.
Any ideas?

asherah

PS : Looks alot like this one : http://reefcentral.com/gallery/showp...t=1&thecat=562