What Is This?

[Bugboy2020]

I saw this attach to my aquarium glass a few days ago. Now it's sent out string-like runners. Why is it?

 

[Remy LeBeau]

Some type of Hydroid would be my guess.

 

[Bugboy2020]

Should I worry about it?

 

[madweazl]

Some type of macro algae?

 

[Ron Reefman]

Hard to say. Looks like some kind of algae to me. Do the 'runners' move? Could they be roots?

If you're concerned, pull it out.