Swimming worm thingy

[cerickson]

Last night when I was checking out my tank, I brought out my trusty red light, and when I did, I noticed that my fish weren't the only things swimming around in the tank..

 

Initially I thought it was one of my small bristle worms that sometimes come loose of the rock and get tossed around in the current until they can grab ahold of something. But no, it wasn't, this thing was swimming. Upon closer inspection, it was white and looked a little bit like a really small bristle worm, but it swam much like a little eel or snake would, squiggling along.

 

Any ideas? I haven't heard of this from anyone in the past.

 

and it only comes out at night and is so small and fast that a pic is pretty much out of the question.