Hydroid?

[MandS]

 

[Syntax1235]

I can't make it out, but looks like there may be some vermetid snails.

 

[DaJMasta]

I can't really tell from the pictures, but I would guess not hydroid. Usually hydroids have a repeating pattern sort of structure or look like individual polyps, and the rougher, less regular, branching appearance of that doesn't say hydroid to me.

Maybe some kind of branching sponge?

 

[MandS]

This is what it does as soon as the lights go out.

 

[MandS]