Top 18 Fascinating Facts About Jellyfish

Digestive System: Jellyfish have a bag-like digestive organ that is more complex than simple sac organisms, with multiple tubes. They possess a mouth and stomach, from which digestive tubes extend to the tentacles for prey capture. Food is first digested outside the cells in the pharynx, then inside the cells in the stomach.

Nervous System: Their nervous network is web-like, resembling a nerve net, but with denser cell concentrations beneath the comb plates. At the mouth area, there are four small nerve ganglia beneath the apex structure. These ganglia are connected by a structure called the statolith, which aids jellyfish in sensing body tilt and maintaining balance.

Reproductive System: Comb jellyfish are hermaphroditic, with two reproductive glands located symmetrically along the digestive tubes, mirroring the symmetry of the stomach.

Small planktonic creatures, such as copepods or larvae from other marine life like fish, shrimp, and crabs, as well as mature comb jellyfish, are captured by the jellyfish’s tentacles. Once the prey is caught, it is directed towards the mouth, with some species even having additional mouth flaps to assist in prey capture. Image of planktonic organisms.

When it comes to the anatomy of a jellyfish, it's remarkably simple. Compared to most animals we are familiar with, jellyfish have a much more basic structure. They lack a brain, heart, bones, or any other essential organs that humans have. Jellyfish belong to the phylum Cnidaria, also known as the phylum of comb jellies, stinging nettles, or sea jellies.

This phylum includes over 10,000 species of aquatic creatures, mostly found in marine environments. Their most notable feature is their stinging cells, specialized for capturing prey. Jellyfish are not considered fish; in fact, they are planktonic creatures, closely related to the microscopic organisms that form the foundation of the marine food chain.

Jellyfish have a surprisingly simple physical structure, with up to 98% of their body composed of water (in addition to some other bodily components). They possess a mouth for feeding and waste elimination, as well as a basic stomach cavity. The final important part of their structure is the tentacles. These vary in length and number, but they are the most critical body part, serving as the primary sensory organs, including providing a form of vision.

When we think about eyes, our natural instinct is to compare them to the human eye, but the variety of visual organs found in nature is vast. There is still much debate about whether eyes evolved once or multiple times throughout the tree of life on Earth. Many agree that some form of light detection mechanisms existed in the earliest ancestors of sighted animals, and the diversity of how genetic programs have developed remains a mystery to researchers.

For jellyfish, they do not possess a brain to process complex visual stimuli. Instead, they rely on simple sensory organs located within their tentacles. Indeed, the sting of a jellyfish that may leave red marks on your skin is also the only way these creatures experience their surroundings and navigate. Sensory organs at the tips of their tentacles can detect light and various chemical cues (like smell) in the water, helping jellyfish orient themselves in space.

Unlike humans, most jellyfish do not have concentrated eyes; rather, their ability to see is created by a network of nerves and proteins known as opsins. Interestingly, not all jellyfish species have the same vision abilities. In fact, some studies have concluded that there are different types of eyes in jellyfish species, each with varying complexity. Jellyfish are skilled hunters, and these rudimentary eyes are sufficient for them to survive and reproduce in oceans worldwide.

Jellyfish reproduce both sexually and asexually. Male and female jellyfish are distinctly different, though hermaphroditic jellyfish have also been discovered.

The lifespan of a jellyfish is typically just a few hours to several months. However, one species has been recorded to live up to 30 years. Jellyfish in artificial aquariums tend to have longer lifespans compared to those living in the wild. They are fragile creatures, easily captured by humans when in their polyp stage (the single-celled organism stage), which is also their most vulnerable stage.

Jellyfish are carnivorous but passive feeders. They consume crustaceans, plankton, fish eggs, small fish, and even other jellyfish. They feed through a mouth located in the center of their body, as mentioned earlier.

Jellyfish are also preyed upon by predators such as sharks, tuna, swordfish, sea turtles, and certain Pacific salmon species.

Jellyfish are without brains, hearts, ears, heads, legs, or bones. Their skin is so thin that they can actually breathe through it.

Although they lack a brain, jellyfish have a simple nervous system with sensory organs that can detect light, vibrations, and various chemicals in the water. These abilities, combined with their sense of gravity, allow jellyfish to navigate and move effortlessly through the water.

Due to the absence of a brain, their movement is limited and largely influenced by ocean currents. Jellyfish don’t actively hunt; instead, they passively wait for prey to come into contact with them. Their tentacles are covered with special cells called Cnidoblasts, which are used for both hunting and self-defense.

Essentially, jellyfish function without a heart. Their outer layer, called the Ectoderm, allows oxygen to diffuse directly into their body, negating the need for a pumping heart to circulate oxygen. Additionally, their digestive system is extremely simple, and both respiration and nutrient absorption don’t require complex organs like a heart.

Jellyfish also have a short, tube-like structure that hangs from the center of their bell-shaped body. This 'tube' serves as both their mouth and digestive organ. In some jellyfish species, this tube is surrounded by a ribbon-like structure that twists in the water, often referred to as the mouthparts or oral arms.

Each jellyfish tentacle consists of thousands of cells called cnidoblasts. Inside each cnidoblast is a nematocyst, a capsule containing a coiled, needle-like thread filled with venom. When prey becomes entangled in the tentacles, the internal pressure causes these needle-like threads to unfurl, piercing the prey like a harpoon. The venom is then injected into the victim.

The primary defense mechanism of jellyfish is to inject venom into potential threats, and their translucent bodies help them remain concealed within the ocean. The tentacles contain numerous microscopic barbed harpoons that are coiled within hollow sacs. When triggered by mechanical or chemical stimuli, the sacs open and seawater floods in, forcing the harpoons to shoot out, penetrate the skin, and inject venom into the target. These harpoons are expelled in less than 1/1,000,000th of a second, making this one of the fastest biological chemical reactions known.

The harpoons can still discharge even after the jellyfish is dead, so it’s crucial to remove any remaining tentacles from the skin. Afterward, rinsing with vinegar can deactivate any untriggered venomous sacs. Seawater can also help remove any leftover venomous sacs.

While some species of jellyfish are beneficial, many others possess venom that can pose a serious danger if stung, especially if not treated promptly. The venom can cause the following symptoms:

• A sting will first cause red, brown, or purple lines to appear on the skin, followed by itching, burning sensations, and even pain or a sharp prickling feeling. Over time, the affected area will swell, and the pain may pulse and spread throughout the stung region.
• If not treated, severe symptoms may develop, including abdominal pain, nausea, dizziness, headaches, muscle cramps, and in extreme cases, difficulty breathing, heart issues, and even death.

On the other hand, jellyfish are considered a nutritious and delicious ingredient in many culinary dishes and have various health benefits due to their high protein and mineral content, including vitamins B, calcium, and iron, as well as other beneficial compounds like sodium, which promote health. Jellyfish can help treat several conditions such as:

• Lowering blood pressure
• Preventing asthma
• Maintaining healthy skin
• Effective weight loss
• Improving memory

Jellyfish are hermaphroditic animals, possessing both male and female reproductive organs located within the digestive cavity, symmetrically aligned with the stomach. Typically, a jellyfish undergoes five stages in its life cycle. First, a mature jellyfish will release eggs and sperm into the water, where fertilization occurs, forming fertilized eggs.

The fertilized eggs develop into small larvae known as planulae. These tiny, worm-like larvae can freely swim in the water. The planula seeks a solid surface, like the ocean floor, to attach to. During this time, it develops its digestive system and starts feeding on its own. Under favorable water conditions and temperature, the planula transforms into a polyp. The polyp then buds off, creating large colonies resembling massive bushes.

When environmental conditions are right, the polyps release multiple young jellyfish. After producing the young, the polyp reverts to a younger polyp form. The juvenile jellyfish continue to grow into mature jellyfish.

Although jellyfish begin their life cycle in a unique way, most species have relatively short lifespans, typically lasting only hours to months. However, some species can live for years. An exception is the immortal jellyfish (Turritopsis Dohrnii), which defies this pattern.

The immortal jellyfish is a species belonging to the Cnidaria phylum, typically found in the Mediterranean Sea and off Japan's coast. It has a bell-shaped body, about 4.5mm in diameter, with a thin membrane, except for a slightly thicker top.

Its stomach is notably large and red. Juvenile jellyfish measure only 1mm in diameter and feature eight tentacles symmetrically arranged along the edge. Fully grown jellyfish, however, possess between 80 to 90 tentacles. What makes the immortal jellyfish remarkable is its ability to reverse its life cycle when injured or facing starvation. Essentially, it can live indefinitely.

When physically harmed or stressed by hunger, the mature jellyfish transforms its cells and circulatory system back to the polyp stage. Lacking tentacles and the ability to swim, it sinks to the ocean floor. Within 24 to 36 hours, this polyp will regenerate into a new juvenile jellyfish and continue to grow from there.

This process is akin to a butterfly's life cycle, where instead of dying, it reverts to its caterpillar stage and emerges from the cocoon to fly again. The “reversing death” phenomenon of the immortal jellyfish is a rare and fascinating example of cellular transformation in the animal kingdom.

Scientific studies suggest that the cells of the adult jellyfish and the polyp are distinct. The transition from adult to polyp allows the jellyfish to create a new body, one that differs from its original form. Despite these changes, the new jellyfish and the old one are genetically identical. This process of life-cycle reversal can repeat itself. In ideal environmental conditions, the immortal jellyfish would never die from old age.

The lion's mane jellyfish is one of the largest jellyfish species, with tentacles that can stretch up to 36.6 meters. Its bell-shaped body can grow to over 2.3 meters in diameter. This species is found in oceans worldwide, and its primary diet consists of small fish, shrimp, and other smaller jellyfish. While its sting is painful, it is not fatal to humans.

The lion's mane jellyfish (scientific name: Cyanea capillata) holds the title of the largest known jellyfish. It is found in cold waters, including the northern Arctic, North Atlantic, and North Pacific oceans, and typically not further south than 42°N. A similar species, possibly the same, lives around Australia and New Zealand.

The largest recorded specimen, discovered along the shores of Massachusetts Bay in 1870, had a bell diameter of 2.29 meters and tentacles that reached 120 feet (37 meters). There is ongoing debate about the classification of this species, with some zoologists suggesting that all species within this genus should be grouped together. However, two distinct types of jellyfish, based on color and size, have been noted in the northeastern Atlantic. The blue variety (Cyanea lamarckii) is smaller (diameter 10-20 cm, rarely reaching 35 cm) and displays a blue hue, unlike the red lion's mane variety.

If you're swimming in the sea and suddenly feel an itch on your leg, it's highly likely you've been stung by a jellyfish. Jellyfish are soft creatures, made up of 95% water and primarily composed of a gelatinous substance called mesoglea. Their delicate structure allows them to survive thanks to the venom stored in specialized cells called cnidocytes, which serve both as protection and as a tool for capturing prey.

The venomous cells can release their toxins even after the jellyfish has died, making it crucial to remove any remaining tentacles from your skin. Rinsing the area with vinegar can deactivate any undischarged venom sacs. Seawater can also help flush out any remaining venomous sacs.

Avoid using fresh water, as the change in salinity can trigger the venom sacs. Folk remedies, like using urine to rinse the sting, could also be harmful depending on its composition. Jellyfish stings can be extremely painful and cause significant discomfort, especially for children. To relieve the pain, reduce swelling, and prevent the toxin from spreading, apply ice to the affected area.

Jellyfish stings can vary in severity. For mild cases, the itching and burning sensation will subside after following these steps. In severe cases, the victim may experience intense pain, swelling, fever, seizures, nausea, or difficulty breathing.

If any of the above symptoms appear, it's essential to seek immediate medical help after performing first aid to prevent further harm to health and avoid life-threatening complications.

Jellyfish are generally known for drifting with ocean currents, but not all of them are as passive as they seem. The Golden Jellyfish, a unique species from the jellyfish family, exemplifies evolution’s adaptation for survival. These jellyfish gather in groups of millions and spend much of their lives migrating in sync with the changing sunlight.

Before sunrise, the Golden Jellyfish gather on the western side of a lagoon and begin their migration around 6 a.m. As the first light of dawn breaks on the eastern horizon, they swim towards the sunlight. They use their bell to pump water, propelling their bodies through the water. Once they reach the eastern shore, they stay there to absorb the sunlight and rest in shaded areas beside the lagoon.

On a distant, beautiful Pacific island, sunlight is abundant, providing a perfect environment for these jellyfish. The Golden Jellyfish not only enjoy sunbathing but need sunlight to survive. Sunlight nourishes the essential nutrients for zooxanthellae, a symbiotic organism that lives within the jellyfish and provides energy through photosynthesis.

At midday, when the sun is at its peak, the jellyfish rest on the eastern shore of the lagoon. But in the afternoon, as the sun begins to weaken and prepare to set, the jellyfish swim back to the western shore, waiting for the next sunrise.

The Box Jellyfish: Known as one of the most venomous creatures, the Box Jellyfish is among the most dangerous sea creatures in the world. It has 24 tentacles, each reaching up to 3 meters long, with over 5,000 stinging cells. Each tentacle contains enough venom to kill 60 people. The toxin is so potent that even a small amount can affect the heart and nervous system, potentially stopping the heart within minutes. If not treated urgently, a sting from a Box Jellyfish can be fatal.

The Lion's Mane Jellyfish: This giant jellyfish, found in the Arctic and the northern Atlantic Ocean, has a bell with a diameter of about 2.4 meters and tentacles that can extend up to 30 meters. It looks like an otherworldly creature, and its venom is strong enough to cause immediate cramping upon contact. This species is one of the deadliest, with its venom being up to 100 times stronger than that of a cobra.

The Irukandji Jellyfish: A close relative of the Box Jellyfish, the Irukandji is much smaller, about the size of a peanut, measuring only 2.5 cm and translucent. Its venom is over 100 times more potent than that of a cobra, delivering a subtle but deadly attack. Both the tentacles and the bell of the Irukandji jellyfish can sting. Victims experience symptoms such as nausea, headaches, arrhythmia, and high blood pressure, which are known as the 'Irukandji syndrome.' If untreated, it can lead to pulmonary edema and cardiac arrest within hours.

The Portuguese Man o' War: This carnivorous jellyfish is actually a colony of organisms living together symbiotically, and it carries one of the deadliest toxins in the world. Its tentacles glow beautifully at night, attracting prey before entangling and stinging them. The sting causes severe pain, fever, and shock, and can lead to respiratory and cardiac failure, often resulting in death.

The Sea Nettle: Also known as the Sea Nettles, these jellyfish have a body resembling a nettle plant. Commonly found in the Chesapeake Bay along the East Coast of the United States, each Sea Nettle has 24 tentacles, with an average length of 1.8 meters. While their venom is not potent enough to kill, their sting causes intense discomfort and pain.

Jellyfish are often admired for their striking beauty, even though many species possess deadly venom. They inhabit all of the world’s oceans and some freshwater lakes and rivers, making them one of the wonders of the underwater world.

Here are some of the most stunning jellyfish species:

• Black Sea Nettle: These giant jellyfish can reach up to 1 meter in diameter, with tentacles extending about 6 meters. They are carnivorous, feeding on larvae, plankton, and even other jellyfish.
• Crossota Jellyfish: Known for their bright red color, these jellyfish have tentacles that resemble the snake-headed Medusa from Greek mythology. Discovered in 2005 in the Arctic Ocean, they are a visual marvel.
• Blue Jellyfish: These jellyfish possess a beautiful color but can cause uncomfortable stings. About 15 cm in length, they can be found along the coasts of Scotland, the North Sea, and the Irish Sea.
• Darth Vader Jellyfish: Found in the Arctic Ocean, this recently discovered species was named after the iconic Star Wars character due to its appearance. It has four tentacles and twelve stomach chambers, and it is venomous.
• Fried Egg Jellyfish: Resembling a fried egg, this species lives in the Mediterranean, Adriatic, and Aegean Seas. Unlike most jellyfish, it can swim independently rather than drifting with the current.
• Purple Striped Jellyfish: This mysterious jellyfish's appearance changes as it ages, and it often coexists with a species of crab in a symbiotic relationship.
• Cannonball Jellyfish: Found along the East Coast of the United States, this jellyfish is named after its cannonball-like shape. It has a unique reproductive method, capable of both sexual and asexual reproduction.
• Flower Hat Jellyfish: These rare jellyfish, found only in the waters of Brazil, Argentina, and Japan, have bell-shaped bodies that resemble ornate hats. Their tentacles coil when not in use, further enhancing their hat-like appearance.
• Portuguese Man o' War: Often mistaken for a jellyfish, this organism is actually a colony of smaller individuals working together. They float atop ocean waves, driven by the wind and currents, and their tentacles can extend up to 20 meters.

Jellyfish inhabit oceans and salty seas, ranging from the surface to the deepest layers. One species, the Peach Blossom Jellyfish, can even be found in freshwater. Jellyfish serve as food for many marine creatures and humans alike. Traditional Chinese medicine suggests that jellyfish, with their salty taste and warming properties, can help detoxify, cool the body, and treat ailments like arthritis.

In some parts of the world, jellyfish are considered a delicacy. Hundreds of tons are consumed annually at a price of around $15 per pound (approximately 0.45 kg). Numerous multi-million-dollar businesses have emerged from the jellyfish trade. The jellyfish typically consumed is the Cannonball Jellyfish.

Jellyfish are also harvested for their collagen, which has numerous uses, including the treatment of rheumatoid arthritis.

They are especially effective in treating conditions like cough, asthma, excessive mucus, bronchitis, sore throat, constipation, bloating, edema, and inflammation. Due to their high economic value, jellyfish were once sold primarily in their raw form at a low cost. However, many businesses now process jellyfish into ready-to-eat products, increasing their value.

Popular jellyfish dishes include:

• Stir-fried Jellyfish with Celery: This dish combines the crunchy texture of perfectly cooked jellyfish with the natural sweetness of celery. The fragrant aroma of ginger and garlic, along with savory seasonings, makes it a must-try.
• Banana Blossom Jellyfish Salad: A visually appealing dish that features crispy, crunchy jellyfish paired with banana blossoms and aromatic herbs, topped with peanuts for added texture.
• Sautéed Jellyfish with Satay: This dish may sound unusual, but once tasted, it’s unforgettable. The tender, chewy jellyfish soaks up the spicy satay flavors, making it a favorite for those who enjoy bold, spicy food.

Ctenophora, or comb jellies, is a small group of marine animals, alongside Cnidaria, making up the Coelenterata phylum under the Radiata group. It is estimated that there are around 100-150 recognized species of jellyfish.

True jellyfish, scientifically classified under the Scyphozoa class, belong to the Cnidaria phylum. This group also includes extinct species like Conulariida, whose relationships remain uncertain and widely debated.

Jellyfish have existed since the early Cambrian period. While they share a similar structure with hydras, jellyfish are better adapted to a mobile, marine lifestyle. As they move, they contract their bell to push water out of their mouth and propel themselves forward. Some species’ tentacles can cause painful stings. Jellyfish lack brains, hearts, and bones.

Distinct features of jellyfish include:

• They live exclusively in the sea, either swimming freely or crawling along the ocean floor with radial symmetry.
• They move by beating specialized comb-like structures made of numerous cilia.
• Their tentacles contain sticky cells to capture prey and defend themselves.
• Although they share several traits with other coelenterates, jellyfish have developed a third germ layer and bilateral symmetry. Unlike other Cnidarians, they lack specialized stinging cells.

When examining the comb jelly's origin and evolution, scientists often compare them to cnidarians, noting that comb jellies possess some older features, such as ciliary transport structures found in certain single-celled organisms. They also exhibit more advanced traits, including definite egg cleavage and early-stage embryonic development. Additionally, unique characteristics such as adhesive cells and cydippid larvae suggest that comb jellies and cnidarians may share a close evolutionary relationship, potentially having a common ancestor.

In particular, scientists are keenly interested in a subgroup of comb jellies that crawl along the ocean floor. These species display bilateral symmetry, with a primitive third germ layer. This developmental feature leads to distinct top and bottom, or front and back, parts of the body. The anterior region is specialized for sensory organs, while the ventral region contains motor and feeding structures. These evolutionary traits have opened up vast possibilities for further development. As a result, some researchers hypothesize that comb jellies could be the common ancestors of all triploblastic animals.

Due to their soft bodies, no fossil evidence has yet been found for this group of animals.

The general shape of a comb jelly is that of a spinning top, exhibiting radial symmetry through the oral-aboral axis. At the aboral end, there is an apex structure that functions as a balancing organ. Along the body, starting from the aboral end, are eight rows of comb plates oriented toward the oral end, each covered with tiny ciliary hairs. Symmetrically placed across the body are two tentacles used for capturing prey, resembling the handles of a vase, with their bases positioned deep within the body. These tentacles are often very long, sometimes multiple times the length of the animal itself. However, some species have shorter or even absent tentacles.

The tentacles of comb jellies are equipped with specialized adhesive cells called colloblasts, which latch onto prey during attack. These cells are shaped like pins with a hemispherical cap and sticky lobes. A coiled and straight filament connects the adhesive cell to the epidermal tissue of the tentacle. When the tentacle touches a prey item, the coiled filament extends, firing the adhesive cell into the prey's body. After release, the adhesive cells are not destroyed and can retract to their original state.

The body wall of a comb jelly consists of two layers of cells with a gelatinous layer in between. This gelatinous layer lacks the muscle cells found in jellyfish and instead contains smooth muscle cells, some of which can be quite large. For instance, in species like Mnemiopsis leidyi, smooth muscle cells have been found to reach lengths of up to 6 cm. The differentiation of these muscle cells and their placement in the gelatinous layer has led some researchers to classify comb jellies as triploblastic animals.