i doubt he will be, but if he is attached DO NOT PULLL!!!!!!! either leave him be or try to pry him off of the bottom glass with a razor blade. make sure you cut/pry as far away as possible if you decide to go this route! if you cut too close or rip anything it will kill the clam.
if he is attached, then that means he is happy, even though they live rockwork more, id leave him in the case.