REMOVE IT!!!.....total damage....
Actually, i've been noticing a couple of my corals have bit and pieces of tissue dangling off them everytime i check my tank in the morning...i've been trying to understand what went wrong...waited in the dark with torches...wakin up in the middle of the night to see what's goin on in my tank when there's total darkness....for a week or 2 i've been doin that with no avail....Anyway, one day as i was doin my routine midnight spot checks, i saw a pincer!!!...oh damn....n' boy is it hard to see them for long...they'll quickly disappear when they sense light....tried searching him in the day in my 16G!!!....but to no success...2 days went by...and it was now obvious it was him, the devil who ate my red brain coral...HALF of it in 3 days!!!...that's like 10 times his size!!!..Had no choice...removed all my occupants and rocks,search through all the rocks with a torch for more then an hour solid before i spoted his hairy lill' leg....After removin em....my corals started to heal...currently fully healed as shown in the pic....
Seriously, REMOVE it...before one of ur prized pieces get munched up!!