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.
Whether a stone will pass on its own depends on its size. 1  Stones smaller than 4 mm: The good news is that about 80% of stones this size will pass on their own. The bad news is that passing a stone takes time -- an average of 31 days.  Stones 4 mm or larger: The chances of passing a stone this size are lower.