Good or bad?

[ahawton]

Just bought a new tank. Was previously established with a different owner.

I found this guy and I am not sure what it is and if it is good or bad? If bad, how should I remove it?

 

[Dburr1014]

That looks like something was there, like it was cut off. Looks like a mushroom base to me.
If you can take the rock out, I'm sure some vinegar and a toothbrush can get it off. Dip the brush in the vinagar, don't splash the vinagar on it incase you have other life on that rock. If you want to rid of it.

 

[fishguy242]

hi,welcome to the reef,
looks like a unhappy nem.

 

[Screwgunner]

Or a spunge was it under the rock?

 

[mdb_talon]

hi,welcome to the reef,
looks like a unhappy nem.

This is my vote also.

 

[vetteguy53081]

May be ball anemone