Could be zoo pox... I'd get them in to a QT tank quickly if you have any other zoas in there. Try 2-4 minutes in a freshwater dip (same temp and ph) then qt them and monitor your other zoas closely.
Also check out http://www.zoaid.com and go to their parasites gallery for pox pix.
Had that same problem on mine that came on a piece of LR I bought. I think they got them because I added more live rock a few months after and my perameters spiked.
Not sure if that was the problem but it might be helpful to you if your water perams are off.