I have a bunch of them, they look like young Anthelia like Guy said. They grow quite rapidly depending on lighting. Mine have taken off like weeds, so I put them in the back corner that gets less light to hopefully slow down their growth.
Definitely not xenia. They will grow in clumps or as part of an encrusting mass, not individually like the polyps you have. I agree with the anthelia guess. They are interesting polyps because if you put them in higher flow, unlike some other corals, they will simply stretch out and grow longer. One question, though, are the arms on the polyps feathery or smooth? That might help answer the question.
I want to also agree with anthelia or a clavularian cousin. I am amazed at how big they can get in larger systems...my current LFS has anthelia rock chunks for sale with polyps nearing 10 inches in length. They are very wavy in the current, and can grow to problematic proportions in some tanks. Sheesh, wish I had that problem with pumping xenia here in Lubbock. There is a particular variety grown here in town that people gladly pay $50 for a couple of tiny polyps, it's the compact and highly-active type of xenia. Cream-colored, very nice but for you guys I bet they are a dime a dozen. The guy fragging them and selling them in town to LFS and friends is likely making a sizeable mortgage payment with the proceeds!
Thanks for all the replies! The polyps seem to doing well and definitely expanding their domain. I found a few other types of polyps on the rock the other days as well. It appears this chunk of rock must have been in the area of polyp city when it was harvested...
Thanx again :!: Below are the current pics of the polyps...