Lacking brains, blood, or even hearts, jellyfish are pretty simple critters. They are composed of three layers: an outer layer, called the epidermis; a middle layer made of a thick, elastic, jelly-like substance called mesoglea; and an inner layer, called the gastrodermis.

How do jellyfish live without a heart?

So how does a jellyfish live without these vital organs? Their skin is so thin that they can absorb oxygen right through it, so they don't need lungs. They don't have any blood so they don't need a heart to pump it.

How do jellyfish live without a brain?

Instead of a single, centralized brain, jellyfish possess a net of nerves. This “ring” nervous system is where their neurons are concentrated—a processing station for sensory and motor activity. These neurons send chemical signals to their muscles to contract, allowing them to swim.