I had some yellow zoas with the long skirts that were slowing disapearing. They would one by one close up, then wither away and die. This happened for a week and I went from 12 to 9 of them, so I started watching at night, and sure enough 2 coepods (thought were nudi's at the time, Im a noob) were coming out, and attacking the zoas. These werent tiny coepods, but where just a little bigger than a brine shrimp. I gave the rock with the zoa's a pods on it a quick freshwater dip, watched the pods fall off and die, and now I back up to 13 of the yellows.