Platyhelminthes Phylum
-In the phylum Platyhelminthes, also known as flatworms, lacks a circulatory system. There are no special organs that species in this phylum contain for circulation. Instead of having a circulatory system, diffusion across the body surface or from the gastrovascular cavity to the body cells fulfills these functional needs. Flatworms have their own system of circulation, which is that they have a gastrovascular cavity with one opening, which eats small worms and insects. Some species in the phylum Platyhelminthes are tapeworms, planarians, flukes, and turbellaria. Due to the fact that none of these species in this phylum contain a circulatory system, they absorb nutrients through their skin and excrete wastes using specialized “flame cells”, which is similar to some species in the phylum of Annelida.
http://www.biology.iastate.edu/Courses/211L/Platyhelm/%20Platyhelminindx.htm
http://www.mcwdn.org/Animals/Flatworm.html
http://www.biology.iastate.edu/Courses/211L/Platyhelm/%20Platyhelminindx.htm
http://www.mcwdn.org/Animals/Flatworm.html