Inverted aiptasia looking alien thing

[Finnjävel]

Love those strange things that can be found in my new reef tank. This one is newest find..

Da fug is this thing? Attached in my sump glass with tentacles. Middle grows some kind of tube.
Another one is reflection from glass. And below is tiny feather duster I think...

 

[brmreefer]

Top one is harmless sponge.

The bottom is a spirorbid worm

 

[Tired]

Top might be a tunicate? Either way, it's a harmless filter-feeder.

 

[Finnjävel]

Thanks for answers. Lets see how big it gets..

 

[Just John]

I think it is the start of cryptic sponges. It will grow new sponges from the tentacle looking things. Here are some I had that got out of control.