ID Please

[Mearle]

I think it's a mushroom but have no Clue it's a new tank the guy gave me this rock and this was on it but it grew I know the green yellow things are sponges well so I hope lol but the yellowish with the brown dots or Spikes is that a mushroom or?? It's very hard to the touch so im unsure any help is much appreciated thanks guys

 

[Reefing Madness]

 

[Mearle]

Anyone?

 

[Mike J.]

It's a Scleractinia, a stony coral. My first thought was it's a Palauastrea which was previously described as a Pocilloporidae but is now considered Astrocoeniidae. So, I think what you have there is a Stylocoeniella cocosensis.