What kind is the respiratory system for roundworms?

Roundworms, also known as Nematodes, do not have a distinct respiratory system. Instead, they rely on diffusion of gases directly through their skin or cuticle. Since they are typically small organisms and have a relatively high surface area-to-volume ratio, diffusion is sufficient to meet their oxygen requirements. Oxygen absorbed through their skin directly reaches the internal tissues, and carbon dioxide is released in the same way. This respiratory mechanism is common among simpler and smaller invertebrates like nematodes.