Weird 8-fold symmetry thingy on my glass

[loneboat]

I found two of these on my glass - looks like it has 8-fold symmetry, and the little arms with "beads" are floppy and flow with the current. They are tiny, maybe half a millimeter across?

 

[MombasaLionfish]

Hydroid.

 

[Reefer1978]

Lookg like a Medusae Hydroid.

 

[loneboat]

Hydroid.

Medusae Hydroid

My googling tells me that these are pests - should I get rid of them? They're tiny, so I assume if I see these two clearly on the glass, I probably have a hundred or so hidden in rock crannies. :-(

 

[MTBake]

Looks like hydroid jellyfish.

They seem to go away on their own, ime.

 

[windemerejack]

Jellyfish, they will die on there own, I had some for about a week/10 days then just started disappearing until all gone, nothing to worry about