Skinny Worm ID?

Somehow, in a bucket of aged tapwater I was about to add to my aquarium I found I strange, very skinny worm. It's about the general size of a bristle worms, and it does, indeed, have bristles, but they are smaller and harder to see than those on other bristleworms I've seen. Also, it has two 'feelers' at its anterior end, and is dark brown rather than orangish. Is it harmful or beneficial? I can't imagine how it got in my water bucket as I always use different buckets to remove old tank water than those I use to add water. But my inclination is to throw it back in my tank (120 gallons). Is this enough of a description for an ID? Thanks.

Yours truly,

John Mayer

Is this even salt water that you are talking about? You state that you were about to add it to your aquarium, but was it top off or change water? If it was fresh I would assume that it was not a marine species.

Either way, it probably wouldn't hurt to add it to your tank. If it is a marine worm it probably came from there, and if fresh something will eat it.