yeah, if you found 3 there are probably dozens more. I've kept Zoas since I started in the hobby and never seen those little buggers until this year. You'll need to check them every day and siphon them off with a baster. They are a royal PITA. Here's a thread with a dip recipe/process to help get rid of them:
http://archive.reefcentral.com/forum...hreadid=451720