TigerIssey
Queen TI
How long has your tank been up and running? Have you recently introduced anything new into the tank?
If these parasitic creatures need a live host to live and breed they don't just appear in a tank for no reason, they are either introduced or come with the LR.
Sorry to be Mr Doom and Gloom and I hope I am totally wrong but I have a bad feeling.
His tank is newly set up 1-2 weeks so it seems to have arrived on the live rock.
He is very good at spotting things (2 mantis shrimp, 1 bad crab, aiptasia and now this), I would think he will be watching like a hawk anyway.
Good Luck Truck.