Organisms in the Phylum Platyhelminthes, commonly known as flatworms, share several characteristics, including bilateral symmetry, bodies that lack internal cavities and central nervous systems. Flatworms and tape worms vary considerably in appearance but share key biological characteristics that distinguish them from worms and other similar species. These organisms live primarily in dirt and soil and inhabit water and land areas around the world.
Bilateral symmetry is a key characteristic shared by these worms. They vary in size from several millimeters to several inches upon reaching adulthood and have bodies containing three distinct and separate layers of tissue. Each layer of tissue contains specific organs and organelles; at the innermost regions are vital organs such as the heart, kidneys, liver and central nervous system. These worms have blind guts, which means that they have mouths but lack anuses. The worms have central nervous systems, as do most other multicellular organisms. However, their nervous systems have longitudinal fibers rather than net shapes. Platyhelminthes have dorsoventrally flattened shapes and reproduce primarily as hermaphrodites. They feed on smaller organisms, including microbes and bacteria, and occasionally consume smaller worms and insects too. Species live in many major habitats, including the digestive tracts and intestines of other living organisms such as many warm-blooded animals and humans.