Platyhelminthes
Animals in the Platyhelminthes phylum, generally made up of flatworms, lack a circulatory system. There are no special organs that animals in this phylum contain to carry out the process of circulation in their body. Rather, diffusion across their body surface or from the gastrovascular cavity to the cells in the body fulfills these needs.
Flatworms have their own system of circulation. In flatworms, they have a gastrovascular cavity with a single opening. At this opening, the flatworm eats small worms and insects. Some species in the phylum Platyhelminthes are tapeworms, planarians, flukes, and turbellaria. Since none of these animals contain a circulatory system, they absorb nutrients through their skin and excrete wastes using specialized "flame cells", similar to some Annelida animals.
Flatworms have their own system of circulation. In flatworms, they have a gastrovascular cavity with a single opening. At this opening, the flatworm eats small worms and insects. Some species in the phylum Platyhelminthes are tapeworms, planarians, flukes, and turbellaria. Since none of these animals contain a circulatory system, they absorb nutrients through their skin and excrete wastes using specialized "flame cells", similar to some Annelida animals.