Mysterious creature

Hi to all of you aquarium enthusiests.
We are new to the hobby and are totally excited about just everything that comes crawling out of our liferock.
Tonight we bought a small rock just because it looked nice. After we placed it in the tank spines came out of the rock and turned into the most facinating neon colors. The whole thing looks absolutly stunning. In the middle there are two long tentacles. If spooked it will retract comletely back into the rock just like a feather duster. It definetly is no feather duster. Has anybody ever seen or come accross anything like it? I guess it would be a good thing to know if we got yourselfs a good or a bad thing here.
As soon as this beauty will come back out of the rock I will post a picture.
Thanks for your help.

 

hi again

 

Just a stab, could be an Anemone. Will wait for a pic.

 

Does it look like any of these comb jellies?

ctenophore - Google Image Search

Some polycheates are also irridescent

Polychaete Annelid Identification, or “You Can Always Tell A Bristle Worm… by Ronald L. Shimek, Ph.D. - Reefkeeping.com

In fact, if it had 5 tentacles instead of two, I would know what it is....a bobbit worm (Eunicid)

 

I don't think it is, but my guess would be a christmas tree worm