We recently had some donated plants spend a night in an unused
aquarium. This afternoon we found some sort of brown worm ... it
seems to burrow in the gravel with one end and at times floats the
other end at the surface (as if breathing through it).

I can't say I've seen anything like this before (science fiction
movies aside, of course) and am wondering what this creature is and if
it's something that's better off dead than in a pond?

Thanks!

http://community.webshots.com/user/steveandtiffany

Click on the pond creature gallery.

-Steve