Name this coral

[sweevo]

Just wondered if anyone could identify the species of coral that i've recently added to my Nano Reef? I think it's a leather coral but I've not had any joy trying to find anything more specific than that. My LFS sold it as a "mixed coral" due to it's neighbour being on the same piece of rock. Here's a pic:

 

 

On a side note, I think i'm going to have to move the coral on the left as it's all but getting swamped by it's neighbour now. I've done a bit of searching on here about frags but have not seen much in the way of a description of taking cuttings. Should I take a cut as near to the base of the coral as possible using say a razor blade? There were dark patches starting to appears on it's surface today which i'm guessing is not a good sign.

 

Thanks.

[Mnesarchus]

Looks to me like a Mushroom leather. Grows big.