Byssus thread mass. Newly acclimated clams are known to discard them. Seemingly for no apparent reason. Some will grow them back, others don't but do just fine without them.
My T. Maxima has done the same thing and is doing great! :)
I do not believe it's the actual foot, byssal organ, just the byssal mass laid down by the clam. If the clams foot is damaged or torn it usually does not end well for the clam, in short order.
Well the clam died the other day. And at the same time I'm not sure why. I'm running 4 bulb t5s, I have a 155 bow face, I had the clam on the sand and I was dosing phytoplankton, calcium at 460, nitrates 0, and everything else is perfect. And I was told that the clam would do fine.. I'm a doing something wrong?
Clams can be tricky initially. If you get another clam try a larger Derasa and see how it does, they are typically less expensive, hardier and some Derasa are quite striking looking.
Place the clam in the sand bed in an area of mod flow and try not to touch it or move the clam.