Platyhelminthes have very soft bodies, which do not preserve as well as fossils. Platyhelminthes are mostly worn like creatures that flattened. Meaning, they look like a ribbon. Due to Platyhelminthes looking like a ribbon, they are called names such as Tapeworm, Flatworm, Fluke, and Planarian. The Platyhelminthes are a successful phylum with around 25,000 known species divided into four classes. The four classes are Turbellaria, Monogenea, Trematoda, and Cestoda. Most Platyhelminthes are parasites on other animals. Only the Turbellarians are mostly non-parasitic. Platyhelminthes are very primitive and creatures that do not have a cardiovascular system or respiratory system. Instead, these creatures diffuse nutrients through their skin and into their body. After these substances have diffused through the skin, their internal organs are bathed in them, and absorb them to be used for regular growth and development. Due to their lack of respiratory and cardiovascular system, there are restricted to their flat shape, which is meant to absorb oxygen and necessary nutrients. These creatures have only one digestive cavity for both the intake and excretion of their food. Platyhelminthes live nearly everywhere, on land, in both fresh and marine waters as well as inside other animals. Most of the free-living species are marine with only a small number inhabiting fresh water.