How does the shape of a flatworms body allow it to rely on diffusion for its respiration and excretion?

Flatworms have a flattened body shape that increases their surface area relative to their volume, facilitating efficient diffusion. This design allows oxygen and nutrients to easily diffuse into their cells from the surrounding water while waste products can similarly diffuse out. Since flatworms lack specialized respiratory and circulatory systems, their thin body enables effective gas exchange and waste removal through simple diffusion processes. Consequently, their body shape is crucial for their survival in aquatic environments where diffusion can meet their metabolic needs.