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.
How Painful Are They? Kidney stones are one of the most common disorders of the urinary tract affecting more than 5% of the population. Fortunately, most pass without intervention. They can range in size small enough to easily pass without detection to large enough to block the passage of urination.