I bought this ecrusting montiopra a month or so ago and noticed there were lots of holes in the rock and the coral itself. After inspection I found nothing. But yesterday, this is what I discovered. :shock:
I had a couple of those in a Christmas Tree rock! Even after the coral itself died, I kept the rock, as the two little buggers were still in it - and the rock is in my sump.
If you have any feather dusters living in the rock...I think these "take over" holes in the rocks.