Unfortunate. I see flatworms and asternia's, but not sure either would have caused such damage......at least not in my experience.
Good luck!
it looks to me line skeletal bail out disorder the flesh might be able to live I would put a cup in the tank and place the surviving tissue in it and see if it lives if it dose it will build a new skeleton
The Asterina is probably just cleaning the area of dead flesh, most likely didn't cause it. The way the flesh doesn't extend onto the bases of the other stalks makes me think it's an alkalinity issue...
With that timing my guess is the ph/alk issues could really be driving it, for some reason euphyllia and mushrooms are really sensitive to those sometimes...
Your lobo is killing the monti
Are stings coming from the lobo or the monti? Could be lobo extending to battle with monti.
I would also cut back monti or just move it.
actually, this is an amazing opportunity, setup a stop motion camera, take a picure every 30 seconds or one minute or something...
(you can get stop motion apps on your phone for free)
it would be amazing to watch the lobo extend them again and work across the monti as it tries to eat it.
you would need a tripod though.