Blood leaves vessels and bathes tissues in sinuses. Blood vessels collect blood and take blood to gills. From gills to heart, to be pumped back out. Open circulatory system has low blood pressure, tissues aren't efficiently oxygenated, animals are slow moving. Waste from coelom into funnel, out other end in excretory pore.
Flatworms have protonephridia are blind tubes that only open to outside.
Flat bodies with 8 separate plates on shell. Torsion - twisting of visceral mass. Larva is bilateral, then one side grows faster than the other. Visceral mass twists 180 degrees, with U- shaped digestive system. Anus above head.