Clam death.

[Slyguy00]

They generally get attacked by snails and other pests on the foot of the clam. I had one that did the same thing, turned out there were a few little starfish and a snail that had made its way into the clam through the bottom and ate it from the inside. Pretty wierd.

[Ryanerickson]

Certain wrasses will inialate clams also I lost 2 clams to a green wrasse