Help ID - coral or pest?

[matlet]

I have had this zoa on my sand bed for some time. When moving it for sand cleaning, there were a lot of bristle worms under the plug. But what caught my attention was between the zoa polyps.

If you look at the picture where my fingers are hidden by the zoa (see blue arrows), is that a mushroom, slime mold or something tied to the bristle worms? Thinking it was slime, I tried to rub it away, but it did not come off.

Any help is appreciated.
Thank you,
Mark

 

[Jikkermanccini]

That is some type of sponge! It's nearly impossible to ID sponge species due to how amorphous they are, but it's likely some sort of photosynthetic sponge based on the color. Whatever the case, it's clearly messing with your zoas so I would suggest trying to scrape off as much as you can and then do a peroxide dip to kill off any remaining damaged cells. It's usually pretty hard to completely wipe out sponges since they can come back from very small pieces.
If you have space in your sump, maybe offload a few of the sponge chunks into some filter mesh or live rock to let it continue its job in the tank. Sponges are known to filter DOCs and maybe even some heavy metals from the water, so you're better off with it than without it.

 

[matlet]

Thank you for a great response.