Editing Circulatory system (section)

===No circulatory system===
Circulatory systems are absent in some animals, including [[flatworm]]s. Their [[body cavity]] has no lining or enclosed fluid. Instead, a muscular [[pharynx]] leads to an extensively branched [[digestive system]] that facilitates direct [[diffusion]] of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. [[Oxygen]] can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out. Consequently, every cell is able to obtain nutrients, water and oxygen without the need of a transport system.

Some animals, such as [[jellyfish]], have more extensive branching from their [[gastrovascular cavity]] (which functions as both a place of digestion and a form of circulation), this branching allows for bodily fluids to reach the outer layers, since the digestion begins in the inner layers.