The Phylum Platyhelminthes:
The phylum Platyhelminthes consists solely of all the different species of flatworms. They are very primitive and uniform creatures that do not have a cardiovascular system or respiratory system. Instead, these creatures diffuse crucial gases and nutrients through their skin and into their body. After these substances have diffused through their skin, their internal organs and structures are bathed in them, and absorb them to be used for regular growth and development. Typical characteristics of the Platyhelminthes are that they are symmetrical invertebrates with unsegmented soft bodies. Because of their lack of a respiratory and cardiovascular system, there are restricted to their flat shape which is meant to absorb oxygen and necessary nutrients. These creatures also have only one digestive cavity for both the intake and excretion of their food. This cavity acts as a mouth and anus, which prevents them from continuously processing their food.