The Human Giant Roundworm is a nematode known as being a major parasite in us humans. It is the largest and most common roundworm found in humans, and is known to infect a sixth of the Earth's population.
It's cardiovascular system (and that of all Nematodes)
The Human Giant Round Worm does not have a true circulatory system. Instead, their bodies contain a pseudocoelom, which is a body cavity located between their epidermises and gut cavity that contains fluid that transports nutrients. From there, they use diffusion to circulate substances around it's body.