Uh, Mouse, look at the pic on the mushroom. Those ARE flat worms. There are some on the leather as well.
mrgoont, take those mushrooms and leather out, dip in a bucket of freshwater with same temp, shake them while you are dipping them in freshwater for about 10 seconds should be able to loosen most of them. As long as the flat worms infestation aren't too bad, the freshwater dip should be able to rid most of them.