Do jellyfish have a heart?

Jellyfish do not possess a heart. Nor do they have blood, a circulatory system, or lungs. Rather, they absorb oxygen from water directly through their epidermis (outer skin layer) in a process known as diffusion. Jellyfish are marine invertebrates with radial symmetry, in which their body parts are arranged uniformly around a central axis, and a simple two-layered gelatinous tissue structure. The simplicity of this organization, owing to several key features, eliminates the need for...