I had the same thing in my poops.
That's a rather big one. I would speculate it is a nematode of some sort.
Try taking some Pin-X or Reese's Pinworm Medicine. They are the same thing, pyrantel pamoate. It is available over the counter. It works on all intestinal nematodes.
If you have a large load of those casings in the next few bowel movements, you will know for sure what it is. Also, if you are experiencing diarrhea on a regular basis, then take pyrantel pamoate, and have a seemingly normal bowel movement, this also indicates worms. This is because the worms died off high enough in the digestive tract to still be completely broken down by your stomach acid and enzymes.
That or you can see a doctor. However, I have tried seeing physicians and they seem to believe parasites
are "a third-world country thing." If you do see a doctor, I suggest finding one that specialized in infectious diseases. Other doctors seem to be a waste of time IMO.