see, it has always been my understanding that xenias werent that easy to care for, but i have three xenia colonies in my 20 gallon tank , and two of them closed up one day, were like this for several weeks, while all my params were normal, and about a week ago, finally started perkign back up again. i just dont know what to make of it. i agree with tjkohler, that if they close up and then begin sliming a brownish color, id pull them out cause your sore than likely going to lose them.
dad, as for mushrooms and xenia, i have one colony that is smack dab in the middle of about 7 shrooms, all of which touch there base, and it is still doing fine. this same colony was also being touched by some yellow zooanthid polyps that seemed to have no effect on it. these yellow zooanthids were at one time stinging my moon coral.!!! MAybe these are just tough little @$$ES!
good luck
jon