Dead Maxima and crocea :( why?

[TonyHNYC]

Hi everyone,
I hope you can help me with this one...I bought 2 clams (a crocea and a maxima) from a reliable source...However, they both died on me with 2 weeks of time..Upon examining the shells, I did not find any snails but a lot of cracks...My other clams (derasas) are doing fine and I don't know why these died on me.. There are some orange spots on the outside shell, this is also where all the cracks seem to be very concentrated and spreading from inside..... Thanks

Tony

 

[TonyHNYC]

here is the outside orange spots. These are NOT coralline algae but were a bit puff up when the clam was alive...

Thanks