Any ideas what this is?

[d0gFartz]

Seen this making it’s way up the back of the tanks glass, about 3/8 inch long

 

[BroccoliFarmer]

I am not getting a clear shot of the head but looks like a hydra worm. I had them. Annoyed me at first but they eventually went away.

How to Identify and Destroy Hydra in Aquarium (In Just Days)

Hydra suck. This small creature eats your fish. You want it removed from your aquarium and QUICK! I'll show you how to quickly identify and kill hydra.

fishlab.com

 

[Sharkbait19]

Could you try to get close up shots of the mouth area?
It looks like it may be a dorvilleidae worm, which is harmless.

 

[Goby Bryant]

Dorvillidae worm