ID?

[dc4]

So, I have had this piece of live rock for about 8 months now and it came with this small, greenish, crator looking thing. At first I didn't really pay much attention to it but it has since grown 2x the original size, encrusting outwards on the rock. Each tiny crevice seems to have polyp type hairs that extend a little out. Any ideas of what it could be? My blenny seems to be investigating it as well but no answers yet...



Sorry for the crappy pics but I only had my phone handy.