What is this ?

[Rmckoy]

I noticed it awhile ago but this was the first tone I was able to get a good picture of it .

 

[ezy33]

My best guess from that photo is it's a feather duster.

 

[czwicky]

Psuedocorynactis. It's a type of pest anemone. I would shoot kalkwasser paste in its mouth to kill it or remove the rock and scrub it if possible

 

[mr_X]

It's not Pseudocorynactis. We don't see pseudocorynactis in our tanks. We only see corynactis, and they don't amount to anything. Nothing to worry about either way.
It's something that filter feeds for sure. My guess would be a filter feeding tube worm also.