Flukes, I believe...liver flukes, because of the color...intestinal flukes are brown, from the pictures I've seen.
And these pictures seem to be of liver flukes that are dead and deteriorated.
Nosing around pictures like this, I once saw a drawing of a cross-section of a fluke. They are fat, not flat.
And, they seem to deteriorate into a flat piece of skin that breaks down quite slowly...like a bit of tomato skin. (Mine were squarish.)
As I understand it, liver flukes LIVE in bile, so are used to it. It seems they are particularly slow to break down.
One article suggested that they attach to the outside of the liver, and hang down. I don't understand how that could be true for any that show up in stool...they would have to have been be WITHIN the digestive system, wouldn't they?
There is no way a dead fluke, or any other dead critter outside the digestive tract, could manipulate itself anywhere except by 'melting'.
We must have wonderful bodies that can break down 'foreigners' outside that tract, and make them disappear...like a sliver in a finger.
All the critters I've seen are pretty tough.
This info isn't very 'scientific'...just things I've read, and guessed.
Good luck, Slimo.