Tiny hitch hiker / coral??

I poked it with a knife on the dull side and it's spongy/leathery. Idk what it could be.
(it's the fleshy looking thing attached to the more left rock, center of the picture.)
((also it's flattened out and doubled in size when the lights are on, when it's dark it curls upwards and gets smaller))
http://i1161.photobucket.com/albums/q506/AzReef7/20120215_170831.jpg
http://i1161.photobucket.com/albums/q506/AzReef7/20120215_170821.jpg

 

It is a Discosoma species mushroom.

 

Pic?

 

The pics are uploaded?

And is this mushroom a good thing? or a pest.
@2in10 Sparks Nevada huh? That's awesome, I lived there for a while, and have many family members there.