I have no idea what kind of algae this is but any help would be appreciated. I've never seen algae of this color before so I would like to know if I should be worried or not.
Looks like hair algae to me, do you have any snails you can place on the clam to eat it?
You could brush it off with a toothbrush for now.
I do know that algae on a clam can kill the clam, but others here will have more experience with clams and algae.