It kinda looks like mesenterial filaments. So interesting that it’s gut tissue would be creeping out the side under the flesh bad; if that’s what it is. Looks like it may have split the flesh band.
Really not sure. If I’m half right, still not sure what that means and anything else is just a guess. Literally everything else appears fine. I see barnacles growing on the outside that would be harmless. The old skeleton looks pretty porous; there could be something there. Maybe something is burrowing from inside out? Remember when I said I would be guessing?
I’d wait it out a couple days if it can handle it. Then I might dip it if I got paranoid. But hopefully someone else can add on.