Wow, I haven't seen one of those in 15 years. That is the notorious Isoclopneous Longa. Aka, the 4 eyed zooxanthellae monster and I can tell he has a full stomach.
OK, just kidding. I have no idea what that dude is, but I'm gonna forward this to someone who can assist you with an ID.
I took some flack a couple years ago for keeping such a sterile tank. By that I mean, everything that goes into my tank, gets a dip. Either medicinally or with fresh water. Corals are simply too expensive and sometime hard to find to risk a serious infestation via pathogen or predator, that could literally wipe out years of investments in time, money etc.
My question to you is this, what are you gonna do with him? And could you give us an idea of the size of this critter?
Thanks for sharing this picture with us. Just goes to show, everybody has something interesting going on or to share with their systems.
Please keep us posted.
Mucho Reef
PS. Lets try to narrow down the reason for your polyp retraction. Lets start with clicking on this link.
http://www.reefcentral.com/forums/showthread.php?t=1852463