Any idea what this is?

[LMG1974]

I received an order today, with a Citron Goby and a Midas Blenny, a pink birds nest and a random zoa frag that they threw in. ( yellow watchman I received was DOA )

when I opened the frag bag to start acclimating, this black ball was wedged between two polyps. If came off easy. It couldn’t be one of the zoa, it was much larger, black. I’m attaching a picture of it and of a stray zoa that broke off the rock.

Does anyone know what it is? Should I keep it or toss it? I’ve been in and out of the hobby and have just never seen this before.

 

[mnat]

When in doubt throw it out. I can't figure it out either, so that makes me not want it in my tank lol.

 

[LMG1974]

That’s what I did. It may have just been a sea squirt. But I would rather get rid of an unknown before it ends up in the tank. Eliminating a possible problem before it gets in is a lot easier than trying to get rid of it after it gets to establish itself and become a real problem.