Well, every tank has worms...
This particular infestation was clearly a parasite/predator of Dendrophyllia. The worms were about a half millimeter in length and were a bright yellow color. They settled in little colony like groups.
On a happy note, I have a bunch of new baby dendro heads that have sprung up on the skeleton left behind. I think it must be some sort of defensive strategy. The worms die once they have eaten all the dendro flesh, and the baby dendros can then grow in place.