My 2 cents- they’re the euphyllia eating kind.
Edit, one of the posts above refreshed my memory, they don’t eat they suffocate by not allowing them to get light.
My 6 line gets picked on or ignored by everyone other than my firefish. But he gets scared by everything. My clowns punk out my six line on a daily basis. But they are animals with unique personalities, so be warned nothing is guaranteed. My yellow tang was a model citizen until the six line showed up. Now the tang is kind of a jerk...
I also just saw the same critter on torch of mine, all other corals look clean... for now. I dipped using Bayer followed by revive. And lightly scrubbed the NON fleshy part of the base base with a toothbrush.
Ive dipped ever Euphyllia that has gone in my tank with bayer followed by revive and some with fresh... I might just have “common” types but the worst reaction I’ve had is a head not opening up for the better part of a day.
If you’re curious the bayer knocked most everything off, only two little buggers came off in the revive and nothing in the fresh...