The Phylum Nematoda:
The phylum Nematoda consists primarily of over 25,000 different species of roundworms. There are some differences between the Nematoda phylum and the Cnidaria and Platyhelminthes phylums, the Nematoda have a proper digestive tract with a mouth and a separate anus. But, just like the other two phylums, the Nematoda dont have a circulatory system either, and supply themselves with nutrients and oxygen through simple diffusion. Nematodes are a very simple organism, that appears to be parasitic amongst most plants and animals, but prefers to life in very moist areas, and cannot survive at all in arid environments. Many Nematoda that are parasitic that normally feast on animals tend to burrow into the skin of animals and enter organs or under their skin. It is here they feast on and absorb materials through diffusion.