To me this looks like a long strand of clotted blood. It does look like it may have segments so it is possible that it has been stained by the Black-Walnut but the Tapeworms I've seen are white or lighter than this.

My acupuncturist called those things big black tar babies, God rest his soul.

My opinion is that is a dead roundorm. I got one just like that a couple of weeks ago. Sometimes roundworm come out deflated and stringy, other times they come out bloated. I was taking psyllium when I got mine, and some would say it was the psyllium, but you could definately see the worm throughout the entire length of the creature. Maybe the psyllium bloats the worms like it bloats us when they ingest it.

The color is very dark, but probably just because you are getting into old junk.

I didn't post the picture of mine at the time, but here it is in case it helps you.....

//www.curezone.org/ig/i.asp?i=56533