Nah, it's a mushroom that bleached out. Prolly won't find out until it gets it's color back. Good luck with it. I got a shroom like that from a dude and it croaked. Not that I was the guy to try to revitalize it in my then swamp tank...
It’s not bleached, it came off a colony of the same mushrooms that were all the same. I can’t find anything that has the small holes in it and google insists a sponge.