What is this?!

[Strangewaterchange]

I just noticed this on my xenia frag that has been there for several months. The only thing I can think of this being is a vermetid snail because it seems like some kind of snail shell and there is definitely something inside moving and it has been there for a while as the xenia is attached. I haven't noticed anything strange other than 1 of 6 zoa frags seems to be strangely shrinking down from 4 to 1 polyp now and it hasn't opened in about a week.

 

[T-J]

Not sure, but it's not a Vermetid snail, I know that.
It's Xenia, pull that piece out and toss it if you're concerned. Xenia is a weed, and will be back in no time.