ID help with brown/black banded growth.

[Ronoc]

Hey. 

I've tried and cannot work out what this is. It has what looks like the underside of a mushroom (like multiple fins) main body and a banded tentacle. I have touched with probe and is is soft but doesn't react.

 

This is in my new 15 litre pico reef. The liverock came from LFS and was well cured. I have a colony of zoas and some GSP. 

I have no recent water parameters. 

Photos r best I can get. 

Thanks

Eamonn

Edited May 2, 2019 by Ronoc
Title upgrade

[Joevember]

Probably a sponge.