ID please! Clear tube, coral, sponge?

[samcurtis07]

Just noticed this growing under a rock of star polyps. Looks to be a rather complex structure growing, although I cannot tell have firm/brittle the structure is. An ICP test kit tested well for everything other than slightly low magnesium, which I have been rising for about a month with increased water changes, so parameters should be fine.

 

[Crabs McJones]

Sponge

 

[Jexter]

Was just about to post a very similar looking white tube like thing hanging all over a few of my zoas (turkey basted them a bit to try to get better pic and see if the tubes 'retracted', thats why they are closed).

So a sponge? Not harmful? it does not seem to be bothering the zoa at all, open and happy all day.

 

[fischtank]

Ever get rid of it?