 Podocytes on the walls of the blood vessels perform first-stage filtration of soluble wastes into the main coelom's fluid.Two metanephridia, each with a funnel-like intake, filter the fluid a second time, returning any useful products to the coelom and dumping the remaining wastes through a pair of nephridiopores beside the anus.There is a nervous center between the mouth and anus, and a nerve ring at the base of the lophophore.