What is this? Green thingy.

[Xanareef]

When we got the rock there were three patches of a light green sponge like material on two of the rocks. I finally figured they were not sponges as they were very hard and felt like skeletons. I assumed they were dead until yesterday afternoon when I was checking out my tank, and voila, it is growing again.

 

It started by peeling off it's old "coating" and now it's growing back, a gauzy coating of what can only be described as green goosebumps. Upon close inspection they are actually polyp like, with different shaped and length tentacles per polyp. It looks as if it's one mat, or carpet, with no individuality. They are so small you have to stick your nose to the tank to tell.

 

Any help would be appreciated. Thanks in Advance

 

Alexis