5 animals that do not have a heart

The heart’s function is to pump blood carrying nutrients and oxygen. Animals that can function without a heart find other means of getting the nutrients and oxygen. These are the animals that do not have a heart.

1. Jellyfish

So how do jellyfish function without a heart?

The function of the heart is to pump blood that transfers oxygen to all the cells in the body. To get the oxygen, jellyfish instead has an outer layer of cells called Ectoderm. Ectoderm absorbs oxygen from the water in the ocean. This Ectoderm layer is very thin and allows oxygen to easily enter. 

The anatomy of jellyfish is quite simple, which makes it easy for the transfer of oxygen from the outer layer of cells to the inner. 

Moreover, 95% of jellyfish mass is water. Only 5% are cells, which means jellyfish does not need much energy to survive and do not need an efficient metabolism.

Just like oxygen, important nutrients are simply absorbed by the outer layers of their body. And the further transfer of nutrients to other cells is made easy by the simple anatomy of jellyfish.

TL;DR (Too Long; Didn’t Read)

Jellyfish do not have a heart. Their outer layer absorbs both nutrients and oxygen present in the ocean water around them. Carrying essential nutrients and oxygen to other body parts is easy due to high water content in jellyfish, and very simple anatomy.

2. Earthworms

If you define heart as a powerful muscle with four chambers, then earthworms do not have a heart. They do have a circulatory system that transfers nutrients to all the cells.

Instead of a heart, earthworms have 5 pairs of arches that are responsible for pumping blood. You may also say that earthworms have 5 pseudo hearts. These arches pump blood into dorsal and ventral blood vessels that carry the blood to and from the body.

The pseudo-heart of the Earthworm lies near its mouth, each in one segment. 

The 5 arches of earthworm that do the work of heart are called aortic arches. There’s one similarity between a vertebrate heart and earthworm aortic arches – the aortic arches regulate the heartbeat with the help of nerve cells. Other annelids, however, use muscle cells to regulate the heartbeat.

TL;DR (Too Long; Didn’t Read)

Earthworms do have organs that pump blood, but that doesn’t fall under the definition of a heart. We can’t decide whether earthworms have a heart or not.

Instead of a standard heart, earthworms have 5 arch pair that pump blood.

3. Sea Spiders

Sea spiders have weak and small hearts that cannot pump blood to the extremities of its long legs. Instead of hearts, sea spiders’ guts contract and relax to pump the blood around the body.

The heart fails to pump blood to the long legs of the sea spiders. The reproductive organs of these spiders are in their legs, making legs too important not to get enough blood.

In fact, sea spiders do not have any lungs either. The respiration take place through their porous exoskeleton.

TL;DR (Too Long; Didn’t Read)

Sea spiders do have a heart but it is weak and small. They are on this list because it is the gut that pumps blood to the extremities of this animal. 

4. Flatworms

Flatworms have no heart and nor do they have any circulatory system. They get oxygen through their skin as and when needed. They transfer of nutrients is intercellular and takes place without any fluid.

Since there is no blood, there is no need to pump blood either. Nutrients get carried to parts that need them through diffusion. Flatworms depend largely on their host for survival. Aren’t they fascinating?

5. Corals

Yes, corals are also animals and they do not have a heart. Let’s see what they need to survive.

Corals do not have internal organs and nor do they need them. Corals depend on algae, zooxanthellae, for their survival. The two are mutually dependent.

The algae live inside the coral and use sunlight to produce energy which is used by the coral. The algae in return get a home to live in and carbon dioxide released by the coral.

TL;DR (Too Long; Didn’t Read)

Corals do not produce their own energy but get energy from the algae that live within them. Hence, they do not need a metabolism, blood, or heart.


  1. Earthworms
  2. Science Daily: Sea spiders move oxygen with pumping guts (not hearts)
  3. National Geographic: Underwater Spider Breathes Through Its Legs
  4. Coral Reef Alliance: What Do Coral Reefs Need to Survive?

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