Secreted by female, shell keeps embryo from drying out. Hangs over, creating a cavity for gills. Radula - rasplike belt of teeth that is used to scrape off algae or eat plants. Not in suspension feeders like clams. Heart pumps blood to aorta and blood vessels.
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.