What's this microscopic worm thing?

[saltyfish24]

I was trying to identify what kind of algae/dino I had, and came across these wriggly worm things. Does anyone know what they are? And what they do?

 

[Jay Hemdal Verified Community Expert]

I was trying to identify what kind of algae/dino I had, and came across these wriggly worm things. Does anyone know what they are? And what they do?

Those look like nematodes. Some are fish parasites, but those won't be found living free in a tank like that, these are harmless.