Thats just a little bit of the corals digestive cavity, they usually expell them if there a little stressed.

One of my hairy mushrooms did this when it got knocked over on its face, was gone the next day and the mushroom is now fine. Another one of my mushrooms did this and then split the next day. Definitely part of the mushroom itself.

I saw them in your tank - they looked great. I thought a worm might have hitchhiked with a piece live rock. After the people saying it is due to the mushroom being stressed, I suspect they are still getting more light them they prefer... I understand the purple mushrooms really prefer shade. I will look closer when I get home, and move the worst off into the shadiest areas and see if that helps. And to think I was worried about not having enough light with that one lonely T5 bulb...

I believe they're called mesenterial filaments

I don't think so. The only time anemones extrude these are when they're fighting another coral that is intruding on their territory or something.

If you've ever fragged mushrooms, you'll see that these are just shroom guts. The fact that the shroom is extruding them makes me think that the underside of the shroom was abraded. Have you recently pressed on the shroom? maybe when you moved it?

I recently got them from noirsphynx (lovely tanks, and their clownfish are breeding) so they got moved around when I placed them into the tank, and probably slid around in the transport bag a bit. Not to mention a 4hr trip home...
How good are the chances of them surviving? I did move them into the shade and they seem much happier already, opening the cap instead of it being all shriveled. The one that was in shade from the beginning is already splitting.

im quite shure thats what the are too,
calfo's book defines mesenterial filaments as internal filamentous material that can be everted defensively with stinging and digestive enzymes

ill just keep calling them mushroom guts since thats what they are

Oops, maybe it's not the mushroom from me then? You must have me an Ed mixed up again, lol. I'm the one that met you at Timmie's.
Mushrooms are pretty hardy so hopefully it should be okay, just don't fuss around with it.

+1. :)