Crocea Clam Problems

[jmor]

I have a Crocea Clam which has attached it self to a flat rock and lies on the sandbed. The outer part of it's shell has this cotton looking thing that is starting to grow and spread all around the outside part of the clam.. I have no pic and this time but will try and get one... does anyone know what this is ?

 

[ReefEze]

Cottony?

Do you have a pic?

What color? White?

RE

 

[epon]

could it be a sponge?