I've had a relatively small gigas in my tank for 5 months. For those of you who have read the stats of my tank below, don't worry, the clam will be moved to a 450g tank in about 6 weeks. At any rate, 2 nights ago when feeding my tank, I saw a small, conical disc of tissue fly out of the clam when it contracted. It always contracts when large food particles land on it, but this did not look like it was rejecting a piece of food. I let it go, but again, last night after adding the food, the gigas contracted and another disc of "tissue" was ejected from the clam.
First, here's the clam
And here's what the tissue looked like after I recovered it from the tank.
It may be difficult to tell in the photo, but it's definately shaped like a cone, and it's quite soft. I had to photograph it in a little bit of water, since it completely lost its shape when it was removed. The fish showed no interest in eating it as it moved around in the tank's current, and the clam looks no worse for losing it. What could it be? I'm pretty certain it's not a component of the food that I add to the tank.