You can also touch it lightly on the side or pass your hand over the top creating a shadow. Both will cause the clam to close quickly which will also help to get any air bubbles out. I do this until the clam has forcefully closed at least three to four times. This is done after I have moved it from side-to-side and around-and-around to get any trapped air out of it.

The best way to move a clam is to never expose it to air. Also make sure there are no micro bubbles in your tank that might get trapped in your clam.

What other inhabitants do you have in your tank? That was an awful quick demise for a clam that was doing so well before. It sounds to me that there may have been something in the tan that attacked or stung the clam which caused it to die so quickly. Just a thought.