16 Jellyfish Facts: They cannot feel the pain

Jellyfish is one of the most gorgeous and interesting creatures on the planet. They have one-of-a-kind features to survive in the ocean and even rule it. Let’s have a look at the jellyfish facts below to see how they can do that!

1. Jellyfish are not fish

The first thing on the list of jellyfish facts is that jellyfish are not fish; although you can see the word “fish” in their name. Jellyfish scientific name is Scyphozoa which means “drinking cup of water” in Greek word. Jellyfish are invertebrates – animals without backbones. They do not have scales, gills, or fins. They swim by opening and closing their “bells.” 

Jellyfish use their tentacles with microscopic stinging cells on them to shock or paralyze their prey before consuming them. Then they move the prey to their mouths with their tentacles and oral arms.

Jellyfish usually eat small fish (larvae), shrimp, crabs, small plants, fish eggs, planktonic eggs, and early stages of many marine species. Jellyfish can even eat other jellyfish! When jellyfish develop blooms, they consume practically everything in the water.

2. Older than dinosaurs

Because jellyfish have no bones, it is difficult to find their fossils. Despite this, scientists have discovered evidence that these animals have been existing in the world’s oceans for more than 500 million years. The jellyfish lineage, it is believed, dates back far deeper, potentially 700 million years or even longer. That’s nearly three times the age of the first dinosaurs.

3. Jellyfish don’t have a heart or brain

One of the weird jellyfish facts is they don’t have brains, hearts, or lungs. Their whole bodies are all about water. The human body is composed of 60% water, whereas the jellyfish’s body is composed of 98% water. Their bodies can quickly evaporate into the atmosphere after washing ashore and vanish in hours after being out of water. 

Jellyfish don’t have lungs because their skin is so thin that they can oxygenate through it. They don’t have a heart because they don’t have blood.

They don’t have a brain, they just have a primitive nervous system with a “nerve net” in the epidermis. Since jellyfish don’t have brains, they are not conscious or can’t recognize their existence. They can’t think or feel pain either.

However, they have some important sensory nerve functions, such as photosensitivity and gravity sensitivity. Even though jellyfish may react to stimuli, this does not imply that they have sentience; single-celled organisms are also capable of doing so.

4. They eat and poop in the same place

Jellyfish do not have separate orifices for eating and pooping. This means that they have one orifice that serves the dual purpose of the anus and the mouth. In other words, jellyfish’s mouth is also their anus. Among those jellyfish facts above, this one is kind of gross.

As a simple animal, the jellyfish lacks a dual-hole system, which evolved much later in evolution. Scientists discovered in 2019 that one jellyfish species produces a new anus with every poop it creates.

5. They’ve made good adjustments to climate change

In contrast to the majority of marine creatures, jellyfish are thriving in the oceans despite the effects of climate change, ocean acidification, overfishing, and a variety of other human influences. This is one of the 16 jellyfish facts helping you understand why they can take over the ocean! 

Corals and jellyfish are in the same Phylum Cnidaria class. While corals are considered to be the most vulnerable to the effects of increasingly acidic oceans, jellyfish are not. You can see how corals are highly affected by climate changes with our guides.

A sight of jellyfish bloom
Jellyfish blooms despite the climate crisis

However, as climate change worsens, experts predict that jellyfish populations will increase in some areas while decreasing in others because of the crisis. They anticipate seeing a gap between jellyfish and other species. For example, jellyfish can survive in low-oxygen environments longer than plankton which is the major food of jellyfish. 

6. Jellyfish can kill you

A crucial thing you should know about jellyfish facts: they can kill you. Despite the gorgeous look, jellyfish are one the most lethal creatures on the planet. All jellyfish have microscopic barbed stingers on their tentacles. Each stinger features a venom-filled bulb and a sharp-tipped tube. Its poison protects itself and kills the prey. 

When you touch jellyfish tentacles, tiny triggers will release the stingers. The tube enters the skin and injects venom. It quickly affects the touch region and may reach the bloodstream. You also can get stung even if the jellyfish is dead. 

Most jellyfish species only produce enough venom to paralyze or kill fish. Jellyfish sting will cause red marks, numbness, itching, pain, or tingling. But some jellyfish can kill you, like box jellyfish. An adult human can be killed in just five minutes by a single sting from the box jellyfish. This jellyfish species is properly the deadliest jellyfish in the whole world. The venom in each box jellyfish is said to be poisonous enough to kill more than 60 people.

The deadly jellyfish of the ocean

Jellyfish stings can be extremely painful for humans and they can kill you before the venom does. Every year, there are approximately 150 million people are stung by jellyfish. However, they do not sting humans on purpose. The majority of stings occur when you unintentionally touch a jellyfish.

If you are stung, sprinkle the area with water rather than rubbing it; doing so may aggravate the situation by activating more stinging cells. Vinegar, various soft beverages (such as Pepsi or Coke), red wine, or even urine can be used to reduce the sting. You should seek immediate medical attention if you notice any swelling or a persistent ache.

Can jellyfish sting each other? Jellyfish may sting other jellyfish, but only while hunting another species. They don’t sting their own species. So how can they do that if they don’t have a brain? According to Southern Fried Scientist, jellyfish have a safety switch. Nothing happens if the sensor detects similar features of their species. Everything else is presumed to be prey or a threat, and it’s worth stinging.

7. They can have eyes

In spite of the simple body, some jellyfish can see. For some species, their vision can be incredibly complex, especially when it comes to night vision. The box jellyfish, for example, has 24 “eyes,” two of which can see in color. 

It’s also believed that this animal’s complex array of visual sensors gives it a 360-degree view of its surroundings, making it one of the few creatures on the planet to do so.

8. Jellyfish can be really small or very big

Some jellyfish are so small they float in the ocean’s currents almost undetectable. The smallest are Staurocladia and Eleutheria, with bell disks ranging from 0.5 to a few millimeters in diameter.

The lion’s mane jellyfish, Cyanea capillata, on the other hand, can extend its tentacles up to 120 feet. The titanic Nomura’s jellyfish, Nemopilema nomurai, is believed to be the world’s largest jellyfish in weight and diameter, and it can dwarf a human diver in size. These monsters can reach 6.5 feet in diameter and weigh up to 440 pounds.

A cameraman is shooting photos of the Lion's mane

The lion’s mane is the largest jellyfish on the planet, with the longest tentacles reaching 118 feet in length.

9. Some jellyfish are immortal

Turritopsis nutricula, a jellyfish species, may be able to live forever. Yes, you heard it right! This kind of jellyfish may never die. Why so?

Whenever this species is threatened, it will undergo cellular reset. This is a process in which the organism’s cells essentially regenerate and become brand new.

Regenerate cell is one of the jellyfish facts helping them rule the sea

The “immortal” jellyfish live in the warm Caribbean and Mediterranean waters. Scientists are studying its unique reset ability in the hopes of understanding how to turn cancer cells into noncancer cells.

10. Traveling in groups is not common

The next thing about jellyfish facts is that they hardly travel in groups. A group of jellyfish is called a swarm, a bloom, or a “smack.” However, you can barely see a group of jellyfish in the ocean. They are solitary creatures who only congregate when they are all pursuing a common food source or when they are all traveling in the same direction along with a single water current.

11. You can eat them

Although jellyfish are not commonly found on restaurant menus, they are edible and are considered a delicacy in some parts of the world, such as Japan and Korea. Jellyfish are usually eaten raw in salads, fried into noodles, or as sushi with soy sauce. Japanese confectioners, on the other hand, have turned jellyfish into candy.

12. Jellyfish can glow in the dark

One special feature about jellyfish is that they can glow in the dark, thanks to a phenomenon called bioluminescence. It is a mechanism that allows them to produce light. 

The bioluminescent organs of many jellyfish emit blue or green light. This light is used to communicate or to frighten away potential predators. Predators are startled by the dazzling flashes of jellyfish like comb jellies.

There are about 50% of jellyfish can glow. Most luminescent jellyfish are found in the deep sea, where nearly every jellyfish can glow.

13. There are 2000 jellyfish types

There are more than 2000 types of jellyfish that are discovered all over the world. Among those 2000 species, only 70 of them can be harmful to you. Here are some jellyfish types:

– Lion’s Mane Jellyfish is the biggest jellyfish in the world. They can be found in the cold water.

– Crystal jellyfish don’t have any color. When bumped, this jellyfish lights green-blue thanks to bioluminescence.

– White-spotted Jellyfish have very weak venom, their stings are harmless to humans. This jellyfish doesn’t use its venom to catch prey! Instead of that, they use a filter system, just like sponges or oysters, to eat microscopic zooplankton.

– Upside-down Jellyfish: these weird jellyfish sit on the ground with their bells, extending their tentacles upward to catch food. To catch food and chase away predators, they release mucus containing venom into the water. When one jellyfish releases mucus, the rest of the colony follows.  This is the reason why even though the venom is not strong, it can still make the water unsafe for small fish.

– Nomura Jellyfish are usually found in Japanese and Chinese seas. When feeling threatened, they will release billions of sperm and eggs which attach to the ocean floor and develop into the new one.

– Atolla Jellyfish (also known as alarm jellyfish): When threatened, the Atolla generates a series of flashes that attract more predators. The theory is that the new predators will be more interested in the first attacker than in the Atolla, giving the jelly a chance to flee!

– Sea Wasp Jellyfish is one of the biggest and the most dangerous jellyfish. Its venom can cause the prey dead in a few minutes. However, this doesn’t work for predators.

14. Jellyfish can clone themselves

Jellyfish reproduction occurs in stages:

Eggs: Adult jellyfish, or medusas, reproduce sexually by releasing sperm and eggs into the ocean. Normally, the fertilized eggs are left to flow freely in the water currents. However, moon jellyfish allow fertilized eggs to stick to their oral arms, where they can be protected from predators until their time comes.

Planula: Planulas attach themselves to a rock, to other structures, or to another animal (like jellyfish) and grow into another stage – polyp, which looks like an anemone-sized creature.

If you cut a jellyfish in half, the fragments can recover and become two new jellies.

Polyp: The process of asexual reproduction takes place throughout this period, which can endure for months or years. The polyps clone themselves and strobilate into another stage – ephyra. Almost all jellyfish species have distinct sexes, which means that the original egg and all future clones will be either male or female.

Ephyra: When the ephyra grows, its bell takes on a distinctive shape, and its tentacles and oral arms develop into species-specific forms. The adult jellyfish is known as medusa.

Medusa: The medusa’s primary purpose in life is to reproduce, therefore jellyfish normally do not live long in this stage. Due to their ability to find the ideal conditions for reproduction, jellyfish do not need long lifespans. As long as the environment is ideal for it to become an adult, it will reproduce as fast and efficiently as it can.

And that’s a jellyfish life cycle!

15. Move like dance

One of the special jellyfish facts is they move as if to dance. When the jellyfish moves, it contracts and relaxes the muscles surrounding the bell. The muscles open and close the bell, pulling in water and then pushing it out again to push them forward. You can see they move in the water in the video below.

Jellyfish travel with the current, therefore if the current reaches the coast, jellyfish may follow. They can also be brought to shore by storms and high winds. Because of their 98%-water body, jellyfish die quickly after washing up on the beach.

16. They have various colors

The last one on the list of jellyfish facts is that they have lots of colors. Some jellyfish are clear, while others come in a variety of brilliant colors. Many of the huge jellyfish have colors such as reds, browns, yellows, mauve, and even numerous hues of blue. 

The sea nettle, for example, is frequently orange or light brown, Octopus jellyfish are blue/gray, and Lion’s Mane jellyfish are golden, just like their name. Many other jellyfish are transparent, allowing you to see their four stomachs.

Depending on the water, jellyfish can take on a variety of colors. Their colors are influenced by their food. Moon jellies, for example, can be pink to purple in hue if they eat a large number of larval crustaceans high in specific pigments.

17. Infographic

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We are passionate animal enthusiasts with over a decade of experience studying animals. With a degree in zoology and conservation biology, we've contributed to various research and conservation projects. We're excited to bring you engaging content that highlights the wonders of the animal kingdom. We aim to inspire others to appreciate and protect wildlife through informative content grounded in expertise and passion. Join us as we delve into the captivating world of animals and discover the incredible stories they have to tell.

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