Unknown rock growth maybe?

Question

saltwater alien?   I have a rock with several mushroom starting on it, but it also has a unknown thing that acts like a coral.  It shrinks when the light goes out and comes out when the light is on during the day.  It was does not seem to bother anything, but I am curious as to what it is. So any help is greatly appreciated in identifying this lil thing!

This is a established tank with fish and several corals in it.  Thanks in advance!

Answer
Hello Fran, its rather hard to tell from the pic but that does appear to look like some sort of large polyp stony coral (lps) in that case thats pretty cool as they are a fairly sought after coral and if you get the right kind they can be quite pricey. if it grows any more that would be awesome. and a great hitchhiker! best of luck to you.

Marcus.