here is what is not adding up- that is a crocea, and a wild one. There are no scutes visible on the side of the vlave, which means it had bored into a rock at one point. It mustve been cut or pryed out. It is also covered in coralline, so it is not recent. I guess it is possible that a fish store sold some guy some live rock with a clam attached- but there is no way this clam came from the ocean on that rock- it was purposefully captured and has since been put onto this rock. That is the possibly the stupidest fish store in the world to not notice that, but anyway, give it good light, stable and suitable ca and alk, and it should be fine- it looks good.