I found this on my zoas. It was hard to get a good picture because they are so small. It looks like some kind of slug with green spots that branch out on its back, it also has little feelers that stick out in front of it like a slug. check the pics out.
Use the search button at the top of the page and search for
zoa eating nudibranch
You should find some information on the and what to do about them. There is some sort of dipping but I can't remember if it is in fresh water or with some chemical additive.
fresh water dip will work, swish them around really good for a few min. You will also have to look for the eggs that are white and in a spiral. If oyu have other zoos, they will need dipped too.
