The blue clam to the left of the tank under the bluejaw?
If so, that looks like a T. crocea to me. I have never heard of a bursa clam, and I believe that the salesperson was blowing smoke.
As for the clam being worth 125, if you like it then yes it is worth it.
Typically these clams sell for $50 to $150 depending on the size, collection point and coloration.
~Michael