Tiny Aiptasia or Hydroid On Glass?

Hi All, Just found this little thing on my glass. I searched around the net but couldn't be 100% sure if these are the clear hydroids that many say will go away on its own, or the more harmful pests that I should get rid of immediately.

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it didn't look like feather dusters and the tentacles look a bit too "brown" for comfort.

Thanks!

EDIT: its about 1/8th inch in size.

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