I’d this for me? Hydroid, aptasia, or something else?

[MoshJosh]

Can anyone ID this for me? (Sorry title auto corrected to “I’d”) Saw this little white guy clinging to a rock. . . If I shine a light on it/or move quickly near the glass it sucks back into the rock.

 

[shakacuz]

could be hydroid or feather duster.

 

[madmarks]

+1 on Feather Duster