Bivalve Hitchhiker on Sun Coral

I have an orange sun coral (Tubastrea) that has never opened much since I got it (several months ago). I always wondered why this particular colony remained closed when all of my others, kept under same conditions, opened fully and fed perfectly.
Today I decided to try repositioning this particular coral and discovered a pretty large bivalve firmly attached. I was stunned that I never noticed this guy before - but i guess it was the way the coral was positioned. The bivalve is definitely alive.
Now I am trying to decide if it is worth prying it free. It's difficult to even distinguish where this thing's foot is. It seems almost melded to the coral!
Looking for opinions.

DSC_0226.jpg

Thanks
PatD