Purple pincushion with parasite or tissue rotting?

[joekidwell]

This has popped up in the past three days, its around the anus area. The anus is still opening and closing but what are the tubes around it and the black discoloration.

 

[Timfish]

Here's my guess. If tissue is lost and it's skeleton is exposed stuff like cyano and other stuff that grows on rock might be capable of attaching and grow. As I don't know what antibiotics would work for it and would not use antibiotics in a tank and moving teh urchin would be a source of stress I'd be tempted to use H2O2. Using a syrenge I would gently apply maybe 5 ml to teh area to see if it clears anything off so I could get a better idea of what's happening.