Please identify

[butwa20]

I got the piece or rock that this clam is on awhile ago I had a small watermelon shrum on it I saw the clam then but never payed attention to it I thought it was just a shell but after stairing at the tank for a while today I noticed it was alive can u please identify it for me.http://i32.photobucket.com/albums/d38/Rentarox123/1300587083.jpg

[SoLiD]

I can't tell from the picture, but there are many different types of clams and oysters that hitch hike on the live rock we buy. All the ones I know of are beneficial filter feeders. Consider it a nice little freebie.

[OrionN]

That is not one of the Tridacna clam. It just one of the common filter feeder calms that clam in the liverock