What is this!?!

[Alexis56]

Yay found this in my reef aquarium this morning! It is latched onto the glass of my aquarium and uses its "tentacles" to move around pretty quickly. I'm afraid this could hurt my livestock. What is it?

 

[bribo12]

Spaghetti worm, completely harmless

 

[Alexis56]

Okay thank you!