How do jellyfish breathe underwater?

Jellyfish, like many other marine organisms, do not have lungs or gills for breathing underwater. Instead, they rely on a simple mechanism called diffusion to obtain oxygen from the water.

Jellyfish have thin layers of cells covering their bodies called epithelia. These epithelial layers are permeable to gases, allowing oxygen from the surrounding water to diffuse into their bodies and carbon dioxide to diffuse out. This diffusion occurs across the surface area of the jellyfish's body.

Since jellyfish are relatively simple organisms with low metabolic demands, diffusion is sufficient to meet their oxygen requirements. They do not actively pump water through specialized respiratory organs like fish do with their gills. Instead, they passively absorb oxygen from the water as it flows over their body surface.