These worm-like creatures are part of this phylum and do not contain a circulatory system. Because these animals do not have a circulatory system, their body passes oxygen and certain nutrients through diffusion (specific particles moving from high concentrations to lower concentrations).
These animals; tapeworms, flatworms, and planarians; have no circulatory system and therefore we can assess that these creatures are less evolved than other animals.
These animals; tapeworms, flatworms, and planarians; have no circulatory system and therefore we can assess that these creatures are less evolved than other animals.