What are these, worms? Fungus?

[MrsJellybean]

I just came back from a 4 day trip and I noticed this white hair like things sticking out of the ground. I thought maybe they were detritus worms at first but they don't match any pics online, and I haven't found anything that looks similar. Any help identifying these would be much appreciated

 

[Innesfan]

Do they appear anywhere else other than the substrate?

 

[MrsJellybean]

Do they appear anywhere else other than the substrate?

No, and I don't see them anywhere else around the tank.

 

[GaryE]

The roots of a plant spreading via runners?