Help ID - small round critter on rock

[austex]

I would appreciate any ideas about this hitchhiker, especially if he is good or bad.
After searching the forum I cannot find an example of this critter that came in on one of my recent rocks. It is small (4-5 mm dia), roundish, centrally located dark spot, with tentacles (?) originating from the circ spot outward.
It reacts to movements by quickly withdrawing its tentacles.

Thanks for the help.

 

[Mike N]

Looks like just a small feather duster of some sort

 

[austex]

Thank you - I was worried it may be some kind of hydroid.
From what I just read about feather dusters they appear to be okay to have in my tank.
Is that correct?

 

[xxkenny90xx]

Your pic is blurry but I'd lean towards feather duster as well. They're good filter feeders

 

[samnaz]

Feather duster. Good filter feeders.

 

[austex]

Thank you everyone for looking at the critter and letting me know.