Science - Nature
By: - at April 3, 2015

15 Remarkable Facts About Jellyfish

Among the remarkable creatures that are lurking in the depths of the sea are the jellyfish, also known as jellies. The gelatinous marine animals belong to the division of animals known by the name of Cnidaria (pronounced with a silent "C"). Found in all parts of the ocean environment, some of the animals even live in freshwater habitats.

By Dan90266 via Wikimedia Commons

The very colorful jellies have been inhabiting seas and streams for hundreds of millions of years. They do not have a brain, skeletal system, heart, or respiratory tract, but possess a highly developed nerve network and tentacles.

Anatomy of Cnidaria Phylum
Anatomy of Phylum Cnidaria


This sensory network of the bell-shaped jelly easily responds to light, odor, and other kinds of stimuli. Jellyfish can live in a variety temperature extremes as well as in a wide scope of saltwater habitats. The marine animals depend on the tides and currents to move horizontally.

15)  Jellyfish Can be Found in Freshwater Ponds and Streams
Typically, jellyfish are associated with saltwater, as the vast majority of the species (particularly the larger types) are found throughout the world’s oceans. The marine animals live in the deep sea as well as on the ocean's surface. You can also find them moving on the currents of freshwater streams.

Craspedacusta sowerbii
By OpenCage via Wikimedia Commons

The freshwater variety are scientifically known as as Craspedacusta sowerbii (C. sowerbii). Beyond the fact that they live in freshwater, the C. sowerbii differ dramatically from saltwater jellyfish in that they feature a solid outer, shell-like layer called a velum. Approximately an inch in size, C. sowerbii are found in freshwater streams and ponds throughout the world.

Known to sting small fish, the freshwater jellyfish also has its own natural predators in the form of geese, turtles, and crayfish.

Should you find jellyfish in a pond, it may have entered the water when it was a polyp, attaching itself to a plant or the bait bucket of a fisherman. Sometimes the animals are transported from flood waters coming from another locale.

Craspedacusta sowerbii
By J. Michael Tracy via Wikimedia Commons

In recent years, freshwater jellies have been found in areas of the world where they had never appeared before. Unlike most saltwater jellyfish, the C. sowerbii are not believed to be a threat to humans.

14)  The Term "Jellyfish" - A Misleading Name
Since 1796, the name “jellyfish” has been a common term. However, the description for the creature has long been considered a misnomer. Jellyfish are not actually fish – in fact, far from it. Due to the confusing and misleading nature of the animal's name, scientists are divided when it comes to determining an appropriate moniker for the creature.

By Papa Lima Whiskey from Wikimedia Commons

Some aquariums have even gone so far as to encourage the public to call jellyfish either “sea jellies” or simply “jellies” as the names are considered to be better describers. Yet, it still is common practice for the animals to be referred to in scientific papers as “jellyfish” and "jellies."

13)  Jellyfish Can Evaporate
Because of their extended and venomous tentacles, jellyfish are ominous threats if you see them while swimming or boating. However, if they happen to wash up on shore, they appear much less menacing. While they can still be dangerous, jellies quickly collapse and almost disappear because of the sun and heat.

That's because jellyfish are comprised of approximately 95% water, and therefore cannot hold their form when they are out of their watery surroundings. It only takes a couple hours for a jellyfish to "evaporate" from view.

Beached Jellyfish
Beached Jellyfish
By BrokenSphere via Wikimedia Commons

Because the gelatinous animals do not possess a skeletal system heart, brain, or respiratory tract, their most significant features, besides their fluid-like form, are basic sensory nerves and a digestive tract.

12)  The Atolla Jellyfish Can Produce Light
The Atolla Jellyfish, otherwise known as the “Alarm Jellyfish," is one of the more unusual and impressive of jellyfish species. The "Alarm" reference is definitely an appropriate descriptive as the Atolla Jellyfish, when attacked, immediately emits a series of flashing lights. The lights, which are caused by a chemical reaction, are released by the energy that is produced when the jelly is attacked.

Atolla Jellyfish

The lights are designed to either startle and confuse an attacker or capture the attention of the attacker's enemies. So, by preying on the Atolla Jellyfish, an animal can also become the target of one of its natural predators.

11)  The Purple Sailor Jellyfish Uses its Body as a Sail
Of the many jellyfish species that are found in the ocean, the Purple Sailor Jellyfish is indeed one of the most unique. Known as the "by-the-wind sailor, the creature can use its body as a sail to drift over the sea. This innate ability allows the inch-sized jellyfish to cover vast distances in its short lifetime - a period that lasts no more than 30 to 35 days.

Purple Sailor Jellyfish Washing up in Oregon
Purple Sailor Jellyfish

Also known as the Velella Velella, the oval jellyfish displays a translucent "sail" and bluish tentacles that are used to sting plankton prey. Unlike the Portuguese Man-O-War, which has a powerful sting, the Purple Sailor Jellyfish is harmless to humans. The fragile and delicate jellies often are blown ashore in tropical locales.

10)  The Irukandji Jellyfish Can Kill Within Minutes
The Irukandji Jellyfish is one of the smallest species of jellies. Although it only measures about a half-inch, it is considered extremely dangerous. Highly poisonous, the diminutive creature is found off the shores of Australia. Because of its tiny size, the deadly yet small animal can also be hard to spot.

Irukandji Jellyfish

Any human stung by the Irukandji Jellyfish will experience Irukandji Syndrome - a comprehensive and complex group of symptoms that occur after the initial sting. After being stung, victims frequently experience vomiting, headache, tachycardia, excessive sweating, and a significant increase in blood pressure. Symptoms can last from several hours to days. Victims, in some instances, may suffer from pulmonary edema, which can result in death.

Also referred to technically as Carukia barnesi, the deadly little jellyfish's name, "Irukandji," is a reference to the Aboriginal tribe that lives in the area where stings are frequently reported. The area is situated in a place called Palm Cover, located off the shore of northern Queensland, Australia.

By Anynobody via Wikimedia Commons

Related to the jellyfish known as the Meduse Della box, the Irukandji Jellyfish was first identified by Dr. Jack Barnes in 1964. The researcher determined a link between the dangerous little jelly and Irukandji Syndrome when he, his son, and a lifesaver were experimentally stung by the thumb nail sized jelly.

9)  Jellyfish Detect Light or Touch with Their "Net" of Nerves
Although jellyfish do not have brains, they still possess certain abilities that are seemingly connected with some type of brain activity. For example, jellyfish can detect light as well as sense touch. They are able to make these distinctions as they possess a "net" of nerves that enables them to react to certain stimuli in the sea.

Moon Jellyfish
Moon Jellyfish
By Hans Hillewaert via Wikimedia Commons

Otherwise, jellies do not have ears, eyes, or a nose as well as no brain or heart. You won't even find a head on the watery and gelatinous creature. Neither do the invertebrates have bones. The gooey creatures do not swim either - they simply drift or float.


8)  Jellyfish Can Still Sting You After They Die
Typically, Jellyfish aren’t just dangerous to people in the water, they can pose an equal threat onshore as well. Jellies can still sting people after they have washed up on a beach and have died. That's because the rope-like tentacles on the creature are still operational after a jelly's demise. Therefore, you can get stung, even if the long, ropy threads, have broken off the jelly's body.

By PretoriaTravel via Wikimedia Commons

Tentacles feature stinging cells called nematocysts, which are used for food gathering and self-defense. When the stingers are triggered, they shoot out from the tentacles, either producing small, irritating stings, or life-threatening rashes and welts. In poisonous jellies, venomous barbs are released upon any type of contact, whether the jelly is alive or dead.

7)  Jellyfish Blooms - A Problem for Commercial Fishermen
Because of global warming, sea temperatures are increasing - all which has caused an overpopulation of jellyfish. In fact, some spots in the ocean feature more jellies than sea. Jellyfish swarms or blooms may extend for vast distances, thereby disrupting the efforts of the fishing trade. Blooms can tear nets as well as consume the large amounts of the zooplankton that is eaten by ocean fish.

Jellyfish Bloom Off Gulf of Mexico
Jellyfish Bloom

In addition, smaller jellies frequently find their way into aquaculture confinements and sting or suffocate fish. Since the 90s, jellyfish blooms have caused the fishing industry problems in such areas as the Sea of Japan, the Baltic Sea, the Black Sea, and the coastal waters off of France and Spain.

jellyfish blooms

However, all that being said, overfishing is the primary reason for the overabundance of jellies. Many of the predators of the jelly, such as tuna, sardines, and herring, no longer thrive as they once did. The smaller fish often ate the larvae and eggs of jellies too, all which cut down on the population of jellies at the time.

6)  Swimming in Jellyfish Lake is Perfectly Safe
At times, the activity of swimming can become a dangerous activity, especially if the swimmer gets stung by a jelly. However, jellyfish stings, which can be deadly, ironically are not a common occurrence in Jellyfish Lake.

Located on the island of Eli Malk in the Republic of Palau, the body of water is an inviting place to swim. That's because the jellyfish that reside in the body of water do not have any stingers.

jellyfish lake

Two types of jellies--known as the Golden Jellyfish and the Moon Jellyfish--have inhabited the lake for over 12,000 years. The two jellies have no known natural predators in the area. As a result, the jellyfish evolved without the need to grow stingers in order to protect themselves.

5)  The Box Jellyfish is the Deadliest of Sea Creatures
While most swimmers are afraid of a shark attack, sharks are not the most harmful creatures in the sea. The Box Jellyfish, also known as the "Sea Wasp," is a greater threat than the shark. In fact, more people are harmed and killed by Box Jellyfish annually. Not only that, the Box Jellyfish is responsible for more human deaths than any other creature in the sea.

Box Jellyfish Warning Sign
Box Jellyfish Warning Sign
By TydeNet via Wikimedia Commons

The Box Jellyfish is driven to feed, based on the nerve impulses in its "net" of nerves. Therefore, the jelly's automatic drive for food causes it to inadvertently attack and kill all kinds of animals, including humans too.

Sea Wasp Jellyfish or Box Jellyfish
Sea Wasp Jellyfish Box Jellyfish
By Avispa marina via Wikimedia Commons

4)  Jellyfish Have Shut Down Power Plants
While jellyfish are often blamed for stings to swimmers and beachcombers, they also have affected people on an even far grander scale. In some instances, jellies have caused the shutdown of nuclear power plants.

For example, in 2013, the Oskarshamn nuclear power plant in Sweden was stalled when a bloom of jellies prevented operations. Literally, tons of the jellies managed to clog the plant's pipes. The occurrence took place when the plant was transferring sea water for cooling purposes. It took days to clean the pipes and for operations to resume.


Jellyfish are not a new problem for nuclear power plants. In 2005, the previously mentioned Oskarshamn plant was shut down when jellies jeopardized plant operations at the time. Also, in 2012, the Diablo Canyon power plant in California ceased operations when jellies stopped up the pipeline. The Philippine island of Luzon also suffered power outages in 1999 when the pipes of the Saul Power plant were, again, invaded with jellyfish. The local citizenry blamed the imminent Y2K virus on the shutdown at the time.

Oskarshamn Nuclear Power Plant
Oskarshamn Nuclear Power Plant
By Daniel Kihlgrenvia Wikimedia Commons

Jellies get into pipelines when nuclear facilities use ocean water for cooling their turbines. According to Lene Moller, a marine biologist who works for the Swedish Institute for the Marine Environment, such occurrences could soon become commonplace, due to overfishing and a lack of monitoring.

3)  Jellyfish Lived with the Dinosaurs
Compared to other creatures, jellyfish don’t seem all that resilient. In reality, though, they are one of the most long-living creatures in the history of the planet. Jellyfish have been around since the time of the dinosaurs.

Mediterranean Jellyfish
Mediterranean Jellyfish

In fact, the oldest jellyfish fossils now date back as far as 700 million years. Prior to 2007, Jellyfish were believed to be around 200 million years old. However, a 2007 fossil find showed that jellies were from 500 million to 700 million years old.

What makes this discovery really remarkable is that jellyfish fossils are incredibly hard to find. Furthermore, these fossils had incredible detailing as they had been preserved in a fine sediment rather than coarse sand over time.

2)  Jellyfish May Solve World Hunger
Because they sting, jellyfish have proven to be, for the most part, a nuisance. Yet they could offer a solution to world hunger too.

Eaten as a delicacy in Japan, jellyfish are dried before they are prepared with a combination of sesame oil and soy sauce. Because of the success of the dish, it has also been served in other countries as well. Dried jellyfish, which can last for weeks, is sold to the consumer food market for consumption too.

Dried Jellyfish
Dried Jellyfish

Because dried jellyfish is a protein-rich and nutritional food, some scientists have suggested that it could be used to solve food scarcities and malnutrition in indigent areas in the world. The only nutritional negative about the food is its higher-than-average content of sodium.

1)  The Turritopsis Nutricula Jellyfish Can Live Forever
Among jellyfish species, the Turritopsis Nutricula is considered immortal - literally. Known appropriately as the "Immortal Jellyfish," the forever jelly can go from one life stage cycle to the next and back again.

Jellyfish typically go through two primary stages of development. The first stage, known as the immature polyp stage, is followed by the medusa stage, where the jelly reaches sexual maturity and dies.

"Immortal" Jellyfish Turritopsis Nutricula
Immortal Jellyfish?

However, in the case of the Turritopsis Nutricula, life does not end after reproduction. The jelly actually has the ability to revert, once again, to the initial or polyp state of development. Therefore, the Turritopsis Nutricula can go back and forth between "youth" and old age. Only the jelly's predators can end its life.

Jellyfish are fascinating, marine-type creatures. Measuring from thumb nail size all the way to the size of a large truck, the animals possess their own definitive and unique attributes and characteristics.





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