Nematodes are one of the most populated phylum in the world. with over 15,000 species of nematoda on the planet that have been discovered, there is still an estimated 500,000 yet to be found. In this Phylum, there are roundworms, gastrotrichs, and also trichina worms. All Nematodes don't breathe in the same way humans and mammals do. They use a process called diffusion where their body takes in oxygen and distributes it to their cells. Because they lack certain major organs that assist breathing in most other animals, nematodes take in oxygen through their skin. The oxygen that is taken in from their skin is DISTRIBUTED from a high lace of concentration to a low place of concentration, which is the cells in their bodies.
The name "nematode" comes from the Greek word "Nema", which means thread. Their name describes them perfectly. Most nematodes have very long, narrow bodies that are virtually the same size as a thread. As one may imagine, the bodies of these animals are not complex, and are quite elementary. However, their bodies are more complex than other worms. With special skins and nerves, nematodes are actually interesting.
To my surprise, Nematodes actually don't have a circulatory system. They move blood, oxygen, and other nutrients through their body by performing diffusion. The circulatory system helps move oxygen and nutrients through the body of an organism. Nematodes don't require circulatory systems because they have other ways of transporting the required amounts of nutrients and oxygen their bodies require.