Aquariums: Unknown worms in tank

Hello everyone. Im setting up a new tank and today I discovered it has worms! They are all over the place in the sand on the wood and swimming in a weird s-shape. There are no fish in the tank yet. The tank has been running for 2 weeks almost 3 now. Im still adding new stuff. The lid is removed so I'm thinking that it could be insect larvae? The last things I added was the wood and the plants. I don't know if the worms came from them?

But anyway could someone ID them? I dont think they are detritus or planaria as they are quite big and thick. Should I keep them around or remove them? Thanks.
I'll add a photo if I can get a good one.