What's growing on my Zoos

[DanG]

Sorry, no pics, my girlfriend is in euqope with my digi cam.
A couple of days ago there were maybe one or 2 of these polyps growing on the same live rock my main zoo colony is attached to. Today there's 10 or 12 of them. They have a small red centre(about the size of a pinhead) and clear feeler tentacles, the whole thing smaller than the head of a pencil eraser.

Any ideas? Nothing new to the tank in the last month or so, water quality is good(N&N both at 0, ammonia 0, calcium 390, dhk 9).