the flatworms you pictured were not planaria and are not the clam eating ones either.......look like plain brown comensal flat worms to me.....clams died for some other reason...

Could the clam have been in a fragile state if it was in a tank infested with them and the trip home they did some more damage?

which store?
 

Don't want to be an ass but what store were they from? If I read correctly was it red coral Edmonton?

Then don't be an ass, I will not say what store except that it was definately NOT Red Coral Edmonton

Correct it was not from us, I was simply trying to help I'd the problem for Greg.....

Steve