Leather Coral ( Sarcophyton Spec) I think.
This Soft leather Coral has been in my tank very much from the beginning, and has done very well. However, it has progressively changed shape over the months. When first introduced, the coral was more cupped in shape, but has since flattened some what. I'm not sure, but I think this may have something to do with my two Percula Clowns which have taken up residents within the coral. The coral receives good flow and lighting.