Clamicide

[mark]

It's the small white Pyramid snail that's known to go after clams, your suspects are more scavengers of the dead.

If it was fairly new wondering about acclimatization as clams can be sensitive.

[Hairytank]

I was worried about the acclimatization of the clam and did a drip from the display over a 1.5 hr period, adding about 2-3x the water volume over this period.
Please understand, I don't want to point fingers, I just want to learn and prevent it from happening again.

Thank you for the replies so far.

[Black Phantom]

It was probably already damaged unless your water parameters are really out of whack. Most healthy clams will close the second a predator gets close. And they close up hard. I accidentaly let a small cleaning brush fall in the tank right on top of my clam. That sucker would not let go. Held on for the better part of a day until it realized the brush was no threat.