Don,
I think what you see there is the Byssal thread bunndle, not the foot of the clam. Maxima and Crocea sometime relaease the entire thread buddle after it was cut. you find that this is just a tendon with a bunch of thread on one end. This is not the byssal gland. Youe clam will be just fine. it will put out more thread to attach itself to a new place.
Minh