Question for the experts, is this a fungal issue?

[Bulldog88]

This sponge looking, also kind of fuzzy stuff is under the mantle. The clam shows no issues, fully open all the time. I'm curious to see what you guys think this is.
Thanks,
Enzo

 

[Bulldog88]

I had to wave my hand over him to get him to close his mantle show you could see the stuff in question.