Thanks, well see what happensMy biggest advice would be the advice everybody on here gives. Only bad things happen quickly in reefing. It will not immediately kill everything. Yes, you should remove it, but take your time. Watch a couple youtube vids on homemade traps. They're noctournal opportunistic omnivores. Should be relatively easy to catch them in a homemade trap at night with a little frozen food in it.
I'm sure if you look up "gorilla crab trap" on YouTube you'll see at least 4 or 5 very usable options. They're incredibly common, and most long term reefers have had one at one point or another.
If it helps ease your mind, I had a tank for almost 4 years with various different fish and corals in it, and I came across a gorilla crab breaking down the tank. Tank was well fed and not casualties.
All that to say don't freak out, take your time, come up with a plan, and enjoy the ride. You'll hit these bumps reefing a lot, and a key to enjoying the hobby is knowing almost nothing is the end of the world and everything can be fixed if you put in the work. Good luck!