WTH..it look like a disease more than an organism that is eating the zoas...
It's the end result of decomposition.
I see this often with anemones that have been treated with antibiotics and have died where i get too lazy to take care of it right away.
In the normal tank, it would have melted but in a condition when only some strains of bacteria are present and the "right" conditions, it creates the white mass and blows off exactly as you have it.
My guess is some of your heads or surrounding tissue died.