Platyhelminthes
This is a phylum that is relatively simple. They are unsegmented and are soft-bodied. They are invertebrate animals which means that they do not have a backbone. The Platyhelminthes also has no body cavities. There is no specialized circulatory nor respiratory system organs. This restricts them to flattened shapes that allow oxygen and nutrients to pass through by diffusion. Platyhelminthes are divided in ways as non-parasitic and parasitic groups. Animals under the Platyhelminthes phyla are very simple organisms.
General Information
Platyhelminthes are mostly seen as worms. They do not have a circulatory system. These creatures have a flat body to cover enough surface area. This is so that they gain the amount of nutrients they need with their body. The way they do this is by diffusion. Diffusion is the spread of particles through random motion from an area of high concentration to low concentration. This is the way that they eat. Their is no main circulatory organ within the flatworm. Yet for special flatworms, they possess a gastrovascular cavity with one opening the eat smalls insects.