what are these? worms?

[zfd6]

i know it's not that good of a pic but what are these? I have seen a few of these in my dsb. One of the larger ones kinda leaves a trail in the sand (when he gets against the glass).
zfd6

 

[nacl-h2o]

You will have many of them, they are a good thing to have. Some are white and some are dark. They are detritus eaters.

 

[ntvflgirl]

I have the same thing. It's kind of cool the way they make a tunnel like that!!