I think I have found out what my nocternal mystery is.
Last night I looked in my tank with a flashlight and saw a small worm about a 1/4" long that unrolled itself like a sock. It was not segmented like a "bristleworm", is this a polychaete?
What you probably saw was a Sipunculan or peanut worm. It is not a polychaete, rather it is in a phylum of it's own. Sipunculans are harmless animals that bore holes in rock and are general surface moppers. For further information on these unique invertebrates, check out:
http://www.aquarium.net/0497/0497_4.shtml,
http://www.animalnetwork.com/fish2/a...wb/default.asp, or
http://www.ucmp.berkeley.edu/sipuncula/sipuncula.html