No Heart, No Brain, No Blood: 20 Facts You Didn’t Know About Jellyfish

Whether they’re simplistic clear blobs marooned on a beach or colorful floaters that form the basis of many nightmares, what are jellyfish exactly?

Let’s take a look at a creature that is significantly more interesting, and unfortunately deadlier, than they appear.

They Aren’t Fish

A jellyfish is certainly gelatinous, but is it a fish? Not at all. A type of zooplankton, it is more scientifically appropriate to refer to them as Jellies, so do so!

What is plankton?

Plankton is typically defined as a type of small or microscopic organisms, drifting or floating in the sea or fresh water. Jellies fall under the phylum of Cnidaria and the class Scychozoa; they exist in an amazing range.

Craspedacusta sowerbii is a freshwater jellyfish in the phylum Cnidaria
Craspedacusta sowerbii

Unlike everything you ever knew, Jellies are even present in some freshwater lakes, such as the Craspedacusta Sowerbii, which has a preference for standing bodies of water.

Jellies Are Very, Very Old

In fact, they are prehistoric creatures, predating even the dinosaurs. It has been suggested that jellies are over 500 million years old, making them the oldest multi-organ animals. It’s even been proposed that jellies could be as old as 700 million years old.

Like other prehistoric creatures, the structure of jellies is very simple. However, the jelly is approximately 98 percent water. That explains why jellies simply evaporate after beaching themselves on sand!

Jellies Sense Their Environment

Jellies are able to detect light, chemicals, and vibrations in the water, but they don’t possess a centralized brain. Instead, Jellies have nerve nets.

What is a nerve net?

A nerve net is a network of neurons that conducts impulses in every direction from a stimulus. They’re common in invertebrates such as flatworms.

Their nerve net enables jellies to sense their environment and also control the actions of their body, just like our brain does. However, they are much more complex and therefore, harder to understand.

Jellies boast three fascinating features: statocysts, rhopalia, and ocelli.

Statocysts are balance sensors that tell the jellies how they are oriented in the water, enabling them to make changes in their position.

Rhopalia receive information in relation to light, chemicals in the water, and movement.

Ocelii are light-sensing organs, the closest things jellies possess that resemble human eyes. While they detect the intensity of light in the environment, they don’t actually allow jellies to see as we know it.

But Scientists Still Don’t Know If They Can See

Box jellyfish, has complex eye-like structures, leading scientists to believe they may be able to see just as we do.

The Cubozoan jellie, also known as the Box jellyfish, has complex eye-like structures, leading scientists to believe they may be able to see just as we do. Their rhopalia contains lenses, corneas and retinas – everything we traditionally believe indicates the ability to see. However, scientists are yet to figure out exactly how jellies interpret these images.

As well as having eye-like structures in its rhopalia, the Box jellyfish also has 24 ocelli. Appearing as dark pigmented spots on the body, the Box jellyfish has more advanced ability to detect light than its gelatinous cousins. It boats a whopping 24 ocelli, meaning it has a 360-degree view of the light intensity in its immediate environment.

They are pretty amazing creatures, but don’t be inclined to touch. With the ability to kill a human in under a couple of minutes, the Box is known as the world’s most venomous marine creature.

Let’s Talk About Bodily Functions

Like the shrimp with its gastrovascular tube, the jelly has what is known as a multifunctional gastrovascular ‘cavity’, which performs all its essential digestive functions in a single location.

Originally, it was believed that the jelly had an orifice that functioned as both the mouth and the anus. However, that isn’t true. Well, it isn’t in the case of the Comb Jellyfish, at least.

Comb jellies are ancient marine predators whose comb-like cilia refract light as they swim.
Comb jellies are ancient marine predators whose comb-like cilia refract light as they swim.

Instead of waste being expelled through its multifunctional orifice, indigestible particles were recently captured on video exiting through what have been deemed as pores. This was a big turning point in what we know about jellies. Scientists propose that jellies, or at least this type, filter waste through specially designed pores. The original video footage showed a tiny ring of muscles surround each pore, leading researchers to believe the comb jellie has a network of sphincter-like holes.

This discovery aligns with what we know about their respiration. Jellies can their oxygen through diffusion, therefore, they don’t need a respiratory system. How is that possible? Simple – they have exceptionally thin skin.

They Mate in Interesting Ways

Jellies can reproduce both sexually and asexually, but the reproductive method of choice depends on the stage of life the jelly is at.

An adult jellyfish reproduces sexually and a juvenile, known as a polyp, is able to reproduce asexually. Polyps are able to clone themselves and the clones then grow into the adult form, which are capable of reproducing sexually.


So how do jellies reproduce sexually, you ask?

After the male releases its sperm through its orifice into the water, the sperm swim into the female’s orifice and fertilize the eggs, but it isn’t as boring as that. One species, Copula Sivickisi, has been seen to do a mating dance as part of its reproductive ritual.

It makes you wonder what other species of jellies do that we just haven’t witnessed!

300,000 Species Remain Undiscovered

Sea Nettle - Chrysaora fuscescens
Sea Nettle - Chrysaora fuscescens

With a current species list hovering at around 2000, there are more undiscovered jellies than there are discovered. It has been speculated that there could be as many as 300,000 species yet to be seen by humans.

And speaking of sight, jellies can be very colorful; it all depends on how deep they live. Jellies that live close to the surface are likely to be colorless; jellies that reside in the depths of the ocean are more likely to be brightly colored.

Jellies Are Big Trouble-Makers

We all know the jelly can pack a sting powerful enough to kill, but did you know that jellies can cause a nuclear power plant to shut down? Nuclear power plants often rely on a seawater inlet as a cooler, and when that body of water happens to possess a bloom, a group of jellies, chaos ensues.

It’s happened internationally, from the United States, to Japan, and even Sweden, jellies are shutting down nuclear plants in record numbers.

Jellies also have the ability to devastate the fishing industry. How? Because jellies feed on fish eggs and larvae, making it difficult for fish to keep their population numbers consistent. That was the case when the Comb Jellie took over the Black Sea, subsequently wiping out their $350 million fishing industry.

Scientists have been developing interesting ways to deal with the threat of jelly blooms. KAIST, a Korean Science and Technology university, has come up with a robot capable of, well, attacking a swarm with a fan blade system. With the ability to destroy 900 kg of jellyfish per hour, it could just be a solution.

Surprisingly, Jellies Have Their Uses

More than 90% of planktonic species are known to produce light, and it is estimated that about 50% of jellyfish are bioluminescent.

What is bioluminescence?

Bioluminescence is the biochemical emission of light by living organisms.

Aequorea Victoria, a bioluminescent hydrozoan jellyfish, is famous for being the source of two proteins fundamental to bioluminescence: Aequorin and Green Fluorescent Protein, also known as GFP.

Aequorea victoria - Crystal Jelly
Aequorea victoria - Crystal Jelly

In 2008, Osamu Shimomura, a Japanese organic chemist and marine biologist, won the Nobel Prize for Chemistry for his work on GFP. Instrumental in the advancement of bio-medical research, GFP can illuminate specific proteins in the human body to track activity in cells. Known as a biomarker, it allows scientists to recognize the activation of genes, making jellies incredibly useful creatures indeed.

And it’s not just their bioluminescence that’s useful. A study of their locomotion, or the way they move, is proving instrumental in the advancement of technology.

Passive Energy Recapture

The structure of jellies enables them to propel their bodies through the water in a pulse-like mechanism. This type of movement is called Passive Energy Recapture; studies have shown it gives jellies a propulsive advantage, allowing them to travel 30 percent farther than they would have been able to otherwise.

This propulsive advantage has been incorporated into technological systems, such as the 170 pound military drone named Cyro. Engineered by Virginia Tech, the purpose of the drone is to conduct underwater military surveillance, underwater mapping, and species observation, in the most intelligent way.

Modeling the design on the efficiency of a jellyfish enables the droid to be energy-efficient, allows it to blend into its environment, and ensures it can operate autonomously.

They Are Also Edible

Scallop with pil pil jellyfish
Scallop with pil pil jellyfish

Jellies have been consumed by humans since approximately 1700, when the Chinese figured out that they made a good meal. Although it might make you feel squeamish, jellies (the non-poisonous ones!) are a highly-revered meal in various cultures.

More than 900 million pounds of jellies are caught for consumption annually worldwide. Humans eat a lot of jellies, it would seem!

So how do you eat them, you ask?

You can buy them fresh, but it is better to buy them dried. Apparently, the older they are, the better they taste. To cook them, all you have to do is rehydrate them in fresh water. Cooking them is a case of a very, very fast boil, just as you would blanch vegetables. If you over boil rehydrated jellies, then they will be chewy and tough – not at all appetizing.

It is important to note that jellies shrink to a tenth of their size when boiled, so you want to prepare your portions taking that into account.

After quickly boiling the body, known as the apron, and the tentacles, you need to slice the jellie as thinly as possible. For the central part of the jellie, you have to roll it tightly, and then slice it thinly.

To enjoy your cooked jelly, marinate it with a typical dressing of rice wine, soy sauce, white vinegar, and sugar. Chill for a while, then along with fresh vegetables, it is ready to serve. It’s almost as if the thinly sliced jellie replaces noodles in a cold dish, and as the jelly does not have a significant taste, you are more likely to taste the marinade you apply to your dish before chilling.

Where can you buy them?

You did ask that, right? You can buy dried jellies at any Chinese supermarket that stocks traditional dried meats and seafood. Buy some today. You’ll be sure to impress your guests with your worldly culinary skills.

The Oldest Recipe

The oldest record of a jellie recipe dates all the way back to the Jin Dynasty in China, dated between approximately 265 to 316 CE. Historians report that jellies were initially preserved with wood ash and salt water, to be consumed at a later date.

If that doesn’t tickle your taste buds, you can try a contemporary alternative. Dried salted jellies are easily purchasable as a snack in any Chinese Supermarket. For the more adventurous, why not try some jellie-based candy?

That’s exactly what students in Japan made to combat their rising jellie population. They collected jellies, which they then reduced to a powder. The powder was then used as the base for delicious caramel-flavored candy.

They Can Make You Beautiful, Apparently

If the idea of a chewy caramel doesn’t tempt you, does the prospect of becoming more radiant tempt you?

Jellies are known for their high level of collagen, which has many uses in the beauty industry as well as in medical science.

And if you’re looking for a new night time routine, you could always treat yourself to a serum made from jellies. If you think that’s weird, consider this.

Coral Eats Jellies

Which situation is more unusual: that humans eat jellies or that coral eats jellies?

Coral typically feeds on microscopic plankton, but apparently, they don’t mind eating the bigger zooplankton, too.

In 2009, researches from Tel Aviv University obtained photographic evidence of a stationary mushroom coral making a meal out of a large moon jellie. There’s also been evidence of sea anemones eating jellies, too.

Jellies Can Be Huge, And Also Tiny

Irukandji jellyfish – The worlds smallest and deadliest jellyfish
Irukandji jellyfish – The worlds smallest and deadliest jellyfish.
Image via ABC Far North: Mark Rigby

The smallest jellie, the Irukandji jellyfish, is very small at around a cubic centimeter in size. It is also conveniently the most venomous box jellie in the world. It causes Irukandji syndrome, a horrific combination of symptoms which left untreated, can cause cardiac arrest and death.

Nomura's Jellyfish - The Worlds Biggest Jellyfish
Nomura's Jellyfish - The Worlds Biggest Jellyfish

The largest jellie, the Nomura’s Jellyfish, is gargantuan in size. It’s hard to imagine a jellie that grows up to 2m in diameter, with a total weight of up to 200 kg. Interestingly, the Nomura is the jellie used in the making of the Japanese candy mentioned earlier.

Still fancy a caramel?

The Most Famous Jelly isn’t really a Jelly

The Portuguese Man O'War, or Blue Bottle (Physalia physalis)
The Portuguese Man O'War, or Blue Bottle (Physalia physalis).
Image via

Everyone is familiar with the distinctive blue huge of the Portuguese man-o’-war. What most people don’t know is that they aren’t jellies, they’re actually siphonophores.

What is a siphonophore?

A siphonophore is an organism made up of tiny individual organisms, named zooids or polyps. They attach to form one organism and function as one; they cannot survive on their own. In comparison, a jellie is a single multicellular organism that can survive on its own.

However, the one thing that this famous siphonophore shares with the jellie is its ability to sting. Their stings are common in the southern hemispheres, and leave the victim with an array of symptoms, some resulting in death.

Their tentacles can reach an astonishing 50 meters in length in total. Although you might see the siphonophore floating towards you, you have no idea where their tentacles actually are, making them a nerve racking visitor to any ocean swim.

The Longest Tentacles Belong to the Lion’s Mane

The longest tentacles come in at a whopping 37 meters long. The largest jellyfish species by tentacle length, Cyanea Capillata’s claim to fame is having tentacles that exceed the length of the largest mammal on Earth, the Blue Whale.
Artist: Ellen Foster / Behance

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The longest tentacles come in at a whopping 37 meters long. The largest jellyfish species by tentacle length, Cyanea Capillata’s claim to fame is having tentacles that exceed the length of the largest mammal on Earth, the Blue Whale.

In 2010, 150 people were stung by the Lion’s Mane on a beach in New Hampshire. The most interesting fact is that the Lion’s Mane was already dead. That’s right – the deceased tentacles of a jellie can still sting.

And not only that.

Lion's mane jellyfish
Lion's mane jellyfish

The reason it was able to sting 150 people was because officials attempted to remove the Lion’s Mane from the water. In doing so, it broke, leaving the deceased parts to float away and sting unsuspecting beachgoers.

Not All Jellyfish Sting… But If You Do Get Stung

Jellies that sting possess a network of cells called nematocysts, used when capturing meals, as their toxins allow them to conveniently paralyze their prey.

Sorry, but it’s a myth that urine will ease the sting from a jellie. If you’ve been stung by venomous jellies, anti-venom is required and it is required quickly. Do not wait around for medical attention, seek it in the first instance.

If the sting is large, it is a good idea to call for emergency first aid. If the sting is small, you should still keep an eye on the victim’s vital signs: check their breathing, ask if they are experiencing chest pain or have any difficulties with swallowing, visually inspect them for hives, signs of weakness, nausea, or any spasms. Any one of these symptoms warrant emergency medical treatment, so seek it.

So how should you treat the area?

If the tentacle is still attached, you will want to remove it, but don’t do so with your hands. To do this, you’ll require some kind of barrier between the tentacle and the person doing the removal.

The most important point is to minimize the contact between the tentacle and the patient’s skin, to avoid any further stings. If no vinegar is available, pure sea water is a good alternative, and it is even more effective when mixed with baking soda.

If you have access to some, an antihistamine in pill form or a hydrocortisone cream will be effective at reducing itching and swelling.

Not So Fashionable Preventative

Who doesn’t worry about getting stung when swimming in an area known for the occasional visit by jellies? The answer to this problem can be found in the weirdest of places, but I can’t promise you that this strategy will enable you to look hot on the beach this summer.

It has been suggested that wearing pantyhose in the ocean, yes those things your mother probably wears to work, or wore in the 1950s, could prevent you from a sting should you find yourself entangled in a stinger’s tentacles.

Not so interested in hosiery?

A full length suit, either a scuba suit or a lycra suit, is also effective at preventing stings, and look slightly better than the results of a raid on your mother’s underwear drawer.
Laughs aside, it’s a worthwhile precaution to take if you do live in a place known for venomous jellies.

Responsible for More Human Deaths than Sharks

Jellies typically kill more humans per annum than even the most dangerous of sharks and they kill in two ways. First and most obviously, some jellies have the power to kill their victim in a minute or two. Other victims die as a result of drowning; one side effect of some stings is paralysis, meaning, you can’t swim. Drowning is inevitable if no one is near to assist you immediately. Suddenly ‘Jaws’ doesn’t seem so scary; they should have made ‘Tentacles’ instead.

So, What Do You Think?

Are jellies much more interesting than you ever imagined?

The next time you see a jellie lingering on the beach or pulsing through the sea, why not lean in for a closer look? And if you’re curious to know more, and you live near a local aquarium, why not find out if they keep a Jelliquarium? If you find yourself in love with jellies, and I don’t blame you if you are, why not keep jellies at home? The oldest, most dangerous, yet simplistic beast deserves to be appreciated by all.

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