Get the over-the-elbow gloves. Get a pair of leather gloves. Put the leather gloves on, put on the over the elbow gloves, and get a friend to hold a strong light where it helps.
Go in after him with a really big net. The gloves are in case of accident, collision, or the need to move a rock. With them, you can wave him into a corner with impunity, or at least less worry.
You need a bucket to receive him, and saltwater prepared. He'll go camo and press himself against a rock: this is how most people get stung.
If you do get stung, the result is about like a fiddleback spider bite: local necrosis, best treated with, I believe, the same thing: one of those Medrol packs and some antibiotic. Go immediately to your emergency room and refer them to fiddlebacks. It works by shutting down the blood supply to the area of the bite/sting, hence the necrosis [dying] of tissue and often subsequent infection. Been there, done that, at least with spiders.
Good luck, hth. Keep a cool head and move with deliberation, never in haste with that fellow: he tires easily.