Also, it you go the tweezer removal route, make sure to get a solid grip on them because their little spines pop right off and they float away to safety on the current.
Looks just like the ones I just had the pleasure of prying off my zoas. If they are all closed up, it’s likely they are getting chomped on. Take a close look at the zoas and you’ll likely see one or two of these guys waste-deep inside a closed polyp. Vigilance will defeat them.