Sorry for the low quality image, but that's the best I can do. SO I first noticed these guys yesterday night in my dwarf white iso culture. There's a relatively good amount of them in there (I can spot them a lot easier than my isos...), and they seemed to pop up suddenly.
I recently expanded my culture by adding so peat moss (microwaved for 2 mins), and I also added in two strips of cardboard (which I didn't sterilize). These are the only two real changes that I've done recently. I feed my isos tropical fish flakes, and the occasional leftover repashy dust.
I don't think they're nemerteans, because they don't move in a "sweeping" motion as has been described in other posts. They are maybe 1-2 mm long (so far) and they appear to be transparent. As in the picture, they not only are in the soil but also climbing the sides of the container. When I opened the lid they did not seem to like the warm air and I think a few of the ones on the sides dried out.
I think that's all the info I have. Are they harmful to the isos? Do I need to restart the culture?