Platyhelminthes are also known as flatworms because they are worms with a flat body. This is the main external morphological feature that differentiates them from nematodes (roundworms).
Even though 85 percent of kidney stones are small enough to pass during urination, fewer than 50 percent of patients chose this option. A person with a normal-size ureter can usually pass a kidney stone with a diameter less than 5 mm (about 3/16 of an inch) without significant pain or risk of kidney damage.
The smaller the kidney stone, the more likely it will pass on its own. If it is smaller than 5 mm (1/5 inch), there is a 90% chance it will pass without further intervention. If the stone is between 5 mm and 10 mm, the odds are 50%.