Hitchhiker on live rock

[JAS1234]

I noticed a small hitchhiker on a piece of live rock. It retracts when stimulated and waves is the circulation. What should I do? It may be an aiptasia but its so small...

 

[saltcreep1025]

It retracts when stimulated and waves is the circulation.

That could be a hundred different things. Can you take a picture?

 

[JAS1234]

Here are some pics. It seems to live in the white tube like structure.

 

[saltcreep1025]

Is this is?

If so it's a feather duster. Worm lives in the tube and catches its food with the "feathers". Perfectly harmless.

 

[JAS1234]

Yes that's it. Thanks for your help.

 

[saltcreep1025]

Quite welcome!