Jellyfish Animal Types, Anatomy, Lifespan, Sting and Facts

Table of Contents

What is a Jellyfish?

Jellyfish also referred to as sea jelly is a free swimmer and gelatinous aquatic animal. These organisms drift through water bodies around the world and as drifters their locomotion is controlled by the flow of the water in which they live. Thus, they are zooplanktonic organisms. The jellies are distinct for their umbrella-shaped bells as well as their long trailing tentacles.

Picture of jellyfish in their habitat

They are ancient animals and have roamed the seas for at least 500 million years. These organisms have effects on the ecosystem in the modern age. They are three times as old as dinosaurs and this makes them the oldest multi-organ animal group. These animals belong to the subphylum Medusozoa which is of the phylum Cnidaria. Usually, the medusa-phase of certain gelatinous organisms of the subphylum Medusozoa are the stages called jellyfishes or sea jellies. Even though a few of them are anchored by stalks to the seabed, the majority of them are free swimmers.

The life cycle of jellyfish is complex. Its medusa is actually the sexual phase in the life cycle of these jellies. This sexual phase produces planula larva that disperses widely and then enters a sedentary polyp phase before it reaches sexual maturity. In most species, the medusae are fast-growing, and within few months they mature, but as soon as they finish breeding they die. The polyp stage, however, is attached to the seabed and may live much longer.

How do jellyfish move?

They can move with the pulsations of their umbrella-shaped bell-like body even though they tend to have limited control over their locomotion. Most of the time, some of them are active swimmers whereas, others largely drift. The umbrella-shaped bell of the jellies can expand and contract to provide propulsion for highly efficient locomotion. These animals don’t need to chase their prey as they possess tentacles that are armed with stinging cells which are used to capture prey and defend themselves against predators.


Globally, jellyfish are found ranging from surface waters to the deep sea. The exclusively marine species of the jellyfish are the Scyphozoans (true jellyfishes) while some of the hydrozoans live in freshwater.

The majority of jellyfishes inhabit marine water, even though a few of them such as the hydromedusae inhabit freshwater. A typical example of a freshwater jelly is a cosmopolitan hydrozoan jellyfish, Peach blossom jellyfish (Craspedacusta sowerbii). This jelly is colorless and is about 2.5 cm (<1 inch) in diameter. Additionally, the peach blossom jellyfish don’t sting.

Some population of jellies has become constricted to coastal saltwater lakes e.g Jellyfish Lake in Palau. The Jellyfish Lake is a marine lake with millions of golden jellyfish horizontally migrating across the lake daily. A few jelly species are usually associated with the bottom of the ocean for much of their lives. Thus, they can be considered benthic. However, many of them live off the ocean floor and thus, form part of the plankton.

In shallow lagoons, the upside-down jellyfish in the genus Cassiopea, for instance, normally lie on the bottom where they sometimes surge gently with their umbrella top facing down. Also, some deep-sea species of scyphomedusae and hydromedusae are normally harvested on or near the bottom of the sea. All of the stauromedusae are usually found attached to something. They are either attached to seaweed, rocky or other firm material on the bottom of the sea.

Some species of sea jellies adapt to tidal flux explicitly. For instance, at ebb tide in Roscoe Bay, sea jellies ride the current until they hit a gravel bar, and then descend below the current. Until the tide rises, these jellyfishes remain in still waters. As the tide rises, they ascend and allow it to sweep them back into the bay. Also, they deliberately avoid freshwater from mountain snowmelt and dive until they discover enough salt.

How do Jellyfish eat?

  1. The tentacles first catch the food.
  2. Then, the oral arms of jellyfishes put the food into the mouth.
  3. The food is digested in the digestive system of the jellies
  4. Excretion of the waste product via the mouth due to the absence of an anus.
  5. Generally, jellyfishes eat their food fast.

The tentacles first catch the food

Jellyfish possess long tentacles that are used to capture their food. Hence, the prey or food of the jellyfish is caught using their tentacles. As planktons pass them, they will stick to the tentacles. For some species, these tentacles can reach up to 100 feet (3 meters). Their feeding habit is rather a passive process where the Jellies just happens to float into their food by chance.

However, as the animal or food touches their tentacles, it gets poisoned as the animal gets paralyzed and is eventually killed so that the jellyfish can eat it. In some bigger jellyfishes, a stinging thread is even curled insides it. These jellyfishes can throw out this stinging thread towards their prey.

The oral arms of the jellyfish put the food into the mouth

The jellyfish has oral arms near the mouth which captures the food and transports it into the mouth. These oral arms are much smaller and shorter than the tentacles. They actively grab the plankton, food, prey, etc., and takes it way up to the mouth. The mouth is directly joined to the stomach and is positioned in the center of the jellyfish.

The mouth of the jellies resembles a little hole and is very simple. This simple mouth only does some basic functions such as directing the food into the stomach as well as shooting out water to propel the body forward. Thus, the mouth also functions in the movement of the jellyfish.

The food is digested in the digestive system of the jellies

Once the food enters through the jellyfish’s mouth,  it ends up in the stomach. The digestive system of this animal is very simple in that it lacks a liver, intestine, and pancreas.

In order to digest the food, this animal makes use of coelenteron which does the same function of the stomach and intestines. The coelenteron has a lot of enzymes that help these animals digest food. Then, through the cells inside the stomach, the food is digested and the rest is spat out again through the mouth.

Excretion of the waste product via the mouth due to the absence of an anus

As jellyfishes feed there will be some food waste of course, but the interesting fact is these animals do not have an anus. Hence, the waste from the food gets out through the mouth: the same way it came in.

Therefore, as water runs in and out of this animal, it will take out the feces. This creates space for the next piece of food that comes along and gets transported into the mouth. The circulation of food and oxygen inside the jellies is done by water in order to give the sea jelly what it needs to live.

Jellyfish always eat their food fast

Generally, sea jellies eat their food very fast. This is because they can’t really swim around with food inside them. Moreover, they only eat tiny stuff so there’s not a whole lot to digest anyway. Usually, they digest their food very quickly because if they have to take large undigested meals around, they wouldn’t be able to float.

What do jellyfish eat?

Jellyfish eat a variety of organisms such as fish, crabs, tiny plants, and shrimp. Usually, they digest their food very quickly because if they have to take large undigested meals around, they wouldn’t be able to float.

Sea jellies do not actively seek food because they rather just capture plankton that floats nearby. However, to get food, these jellies can propel themselves. They have 4-8 oral arms that capture food from the tentacles and into their mouth.

The sea jellies, in turn, are also eaten by other animals such as spadefish, sea Turtles, sunfish, other jellies as well as humans. Jellies are very unique as they tend to eat anything that comes their way depending on their size. Let’s look at what these jellyfishes eat based on their sizes i.e bigger and smaller jellyfish.

What the small jellyfish eat

  • Fish eggs
  • Plankton
  • Tiny fish
  • Aquatic Plants
  • A ton of other tiny creatures

Listed above are some of the organisms that the smaller jellyfish eats. They feed on all the different tiny organisms you can find floating around in the sea. Therefore, in areas that a lot of jellyfishes inhabit, smaller fishes are affected because these jellies usually eat everything that is small and has nutrition.

As a result of too many jellies, the smaller fish has to go somewhere else in order to find food. When there are a lot of sea jellies swimming together, it is called a jellyfish bloom. A jellyfish bloom can consist of millions of jellies and this usually causes problems for fishermen as well as fish. However, when this happens, one just has to wait till the current carries the jellyfish in another direction.

What big jellyfish eat

  • Aquatic plants
  • Lobsters
  • Crabs
  • Shrimps
  • Barnacles
  • Other Jellies

Listed above are some of the organisms that the bigger jellyfish eat. The majority of them with their venomous sting can actively capture and kill bigger organisms. Once an animal triggers the sea jelly by touching its long tentacles, it shoots out its sting. It then gets the animal into the mouth, once it has captured and paralyzed the animal with its sting. The sea jellies tend to have cannibalistic behavior and are really not aware of what enters into the mouth. Thus, it feeds on whatever floats by.

How do Jellyfish reproduce

The life cycle of jellyfishes is complex. During a single sea jelly’s lifetime, it can reproduce sexually and asexually and takes on two different body forms. The adult form of an adult jellyfish is called a medusa. This medusa is the umbrella-shaped form that is seen in the water.

Through spawning, medusa jellyfish reproduce sexually. Spawning is the mass release of eggs and sperm into the open ocean. Sometimes, the entire jellyfish population spawns together. From their mouth, the male and female release the sperm and eggs respectively. Fertilization in most species takes place in the water whereas, in others, the sperm swim up into the mouth of the female and fertilize the eggs within.

Then, the fertilized eggs develop into planulae. The planula is a ciliated free-swimming larva that is shaped almost like a miniature flattened pear. Then, the planulae attach to a firm surface after several days of development and transform into flower-like polyps. These polyps possess a mouth and tentacles that they use to feed on zooplankton.

The Polyps, however, reproduce asexually by budding. Budding occurs when the polyp divides in half to produce a new genetically identical polyp. Alternatively, depending on the type of jelly, they can produce or transform into medusae. For instance, the Hydrozoan polyps bud medusae from their sides whereas, each cubozoan polyps transform into a medusa.

A process takes place in scyphozoans called strobilation. A polyp during strobilation splits into ten to fifteen plate-like segments which are stacked on top of one another in a tower referred to as a strobila. However, a juvenile jellyfish is formed after a segment separates from the strobila and it is called an ephyra. Then, the ephyrae develop and mature into the medusa form. Therefore the basic life cycle includes:

Egg —> Planula larva —> Polyp —>Ephyra —> Medusa.

The medusa is the sexual stage and sometimes the polyp stage is secondarily lost.

Life cycle

A diagram showing the Life cycle of Jellyfish
A diagram showing the Life cycle of Jellyfish
Photo credit:

The lifecycle of a jellyfish is complex and includes sexual and asexual phases with the medusa in most cases being the sexual phase. The eggs of the jellies are fertilized by the sperm and develop into larval planulae as seen in the diagram above. These larval planulae further develop into polyps and bud into ephyrae. Then, the ephyrae transform into adult medusae. However, it is important to note that certain stages may be skipped in some species.


Once jellyfishes reach adult size and there is a sufficient supply of food they spawn regularly. However, spawning in most species is controlled by light as all individuals are seen spawning at about the same time of day. In most cases, this timing is usually at dawn or dusk. As adults, jellyfish are either male or female and occasional hermaphrodites.


These adult jellies release sperm and eggs into the surrounding water. The released eggs are then fertilized by the sperm and develop into planula larvae. This egg stage is the first phase of the jellyfish life cycle.

However, how these eggs get fertilized varies in various species. For instance, in few species, the sperm swim into the mouth of the female and fertilize the eggs within her body. It is in her body that the fertilized eggs stay during early developmental stages. In moon jellies, on the other hand, the eggs stay in pits on the oral arms. These oral arms thus serve as a short-term brood chamber for the developing planula larvae.


The planula is a ciliated free-swimming larva that is shaped almost like a miniature flattened pear. This small larva is covered with cilia and when it is sufficiently developed, it settles onto a firm surface. The planulae attach to a firm surface after several days of development and transform into a polyp.


The polyp is made up of a small stalk which is topped by a mouth that is ringed by upward-facing tentacles. These polyps may be sessile or free-floating and resemble those of sea anemones and corals. This polyp stage may live on bottoms, boat hulls, or other substrates as sessile organisms or as free-floating organisms, they attach to tiny bits of free-living plankton, fish, or other invertebrates. They may be colonial or solitary. The majority of polyps in diameter are only in millimeters and they feed continuously. This polyp stage may even last for years.

Then, the polyp after being stimulated by seasonal or hormonal changes may begin to reproduce asexually by budding. In the Scyphozoa, this is called a segmenting polyp or a scyphistoma. As a result of budding, more scyphistomae, as well as ephyrae, are produced.

Depending on species, the budding sites vary. In some species, the budding site could be the manubrium, tentacle bulbs, or the gonads of hydromedusae. Moreso, the tentacles of the polyp are reabsorbed in a process known as strobilation where the body starts to narrow and form transverse constrictions. There are constrictions in many places near the upper extremity of the polyp. Then, separate segments known as ephyra detaches as the constriction sites migrate down the body.


The ephyrae are free-swimming precursors of the adult medusa stage. Therefore, the adult medusa stage is the life cycle phase that is typically identified as a jellyfish. The ephyrae swim away from the polyp and grow. It is usually only a millimeter or two in diameter prior to growth.

However, there are some distinct species that may skip some of these basic stages. For instance, the Limnomedusae polyps can asexually produce a creeping frustule larval form. This larva crawls away and then develops into another polyp. Also, a few species by budding directly from the medusan stage can produce new medusae. Furthermore, through fission, some hydromedusae can reproduce.

Anatomy of a Jellyfish

When talking about the anatomy of a jellyfish, the body description and part is usually quite brief. This is because they are quite simple compared to the vast majority of animals in the ecosystem. They lack a brain, a heart, bones, and every other important organ that other animals and humans have.

As members of the Cnidaria phylum, they can’t be classified scientifically as fish that belong in the phylum Chordata. Actually, the sea jellies are a type of plankton and are even more related to corals and sea anemones rather than fish.

The body of these animals is mainly made up of water with few body parts. They are basically composed of two cellular layers: the outer epidermis and the inner gastrodermis layer. However, in between these two cells is a thick jelly-like fluid referred to as the mesoglea. This is how they got their name:- jellyfish.

These animals have a single opening that functions as both a mouth (orifice) and an anus. The opening as a mouth takes food in and as an anus excretes the waste food out. A rudimentary stomach is part of the anatomy of a jellyfish. The mouth leads to the gastrovascular cavity which is a rudimentary stomach. Digestion and absorption of nutrients from the food take place in the gastrovascular cavity.

Another important element of the physical structure that makes up the anatomy of a jellyfish is the tentacles. The tentacles are the most crucial body part of any sea jelly and can vary widely based on length and number.


The main body form of a true jellyfish is the umbrella-shaped bell. This is a hollow structure that contains a mass of mesogloea. The mesogloea is a transparent jelly-like matter that forms the hydrostatic skeleton of the sea jelly. Water forms about 95% or more of the mesogloea. Also, the mesogloea contains collagen and other fibrous proteins. There are wandering amoebocytes as well in the mesogloea that can engulf debris and bacteria. On the outside, an epidermis borders the mesogloea while the gastrodermis borders it on the inside. The edge of the umbrella-shaped bell is usually divided into rounded lobes called lappets. These lobes allow the bell to flex. There are dangling rudimentary sense organs called rhopalia in the gaps between these lappets. The margin of the bell usually possesses tentacles.

Manubrium and mouth

There is a stalk-like structure on the underside of the bell that hangs down from the center called the manubrium. It hangs from the center together with the mouth and serves as the anus, at its tip. Connected to the manubrium are four oral arms that stream away into the water. The mouth opens (leads) into the gastrovascular cavity. Digestion takes place in the gastrovascular cavity and nutrients are absorbed there.

Four thick septa subdivide the gastrovascular cavity into a central stomach and four gastric pockets. Attached to the septa are the four pairs of gonads and close to them are four septal funnels that open to the exterior, probably supplying good oxygenation to the gonads. There are gastric filaments near the free edges of the septa that extend into the gastric cavity. The gastric filaments aid in subduing and digesting the prey as they are armed with nematocysts and enzyme-producing cells. The gastric cavity in some scyphozoans is joined to radial canals which branch broadly and may join a marginal ring canal. In these canals are cilia that circulate the fluid in a regular direction.


Similar in structure to the true jellyfish is the box jellyfish. The box jelly as its name implies has a squarish box-like bell. From each of the four lower corners, a short pedalium or stalk hangs. Attached to each pendalium are one or more long slender tentacles. A shelf known as a velarium forms as the rim of the bell is folded inwards. The velarium restricts the aperture of the bell creating a powerful jet when the bell pulsates. Thus, allowing the box jellyfish to swim faster than true jellyfish. Even the nematocysts that sting are located mostly on the tentacles. However, true jellyfishes have them too around the mouth and stomach.

Hydrozoans are similar also as they normally have just four tentacles at the edge of the bell, even though many of them are colonial and may not have a free-living medusa stage. A non-detachable bud in some species referred to as a gonophore is formed. It contains a gonad with many other medusal features such as tentacles and rhopalia absent in it.  The jellyfish in the class Staurozoa are attached by a basal disk to a solid surface resembling a polyp. The oral end of the stalked jellyfish is partially developed into a medusa that has a central manubrium with a four-sided mouth and tentacle-bearing lobes.

Absence of respiratory, circulatory system and brains

Most jellies do not have a central nervous system with no specialized systems for osmoregulation, respiration, and circulation. The sea jellies have no blood or vessels, thereby there is no actual circulation system in place. Also, the sea jelly does not have a specialized system for respiration because sufficient oxygen diffuses through their epidermis.

The rhopalia in sea jellies contain rudimentary sense organs that are able to detect an odor, light, water-borne vibrations, and orientation. Traditionally, jellyfishes are thought to lack a central nervous system. However, they have a loose network of nerves called a nerve net which is located in the epidermis. This nerve net concentration and ganglion-like structures could be considered to constitute a nervous system in most species. A sea jelly can detect stimuli as well as transmits impulses. Impulses are transmitted all over the nerve net, around a circular nerve ring, and to other nerve cells. Moreso, the rhopalial ganglia has pacemaker neurons that control swimming direction and rate.

The rhopalia in many sea jelly species include ocelli which are light-sensitive organs that can distinguish light from dark.  With heavy crystals at one end, the rhopalia are suspended on stalks acting like gyroscopes to set the eyes towards the sky. For instance, some kind of sea jellies looks upward at the mangrove canopy as they make a daily migration from mangrove swamps into the open lagoon. They feed in the open lagoon and then go back again to the mangrove swamps.

Compared to other types of jellyfish, Box jellyfish have a more advanced vision. Each individual of the box jellyfish has 24 eyes. Two of these eyes can see color as well as four parallel information processing areas. This supposedly makes the box jellyfish one of the few animals to have a 360-degree view of their environment.

Do jellyfish have brains?

Jellyfish don’t have brains, rather, as discussed earlier they have a network of neurons; a nerve net. The nerve net allows these animals to be sensitive to their environments. They are sensitive to changes in water chemistry or the touch of another animal that indicates the presence of food.

There are some specialized structures such as statocysts in the nerve net which serve as balance sensors. They help the sea jellies to be able to know whether they are facing up or down. Also, the light-sensing organs called ocelli in the nerve net can sense the presence and absence of light.

Additionally, rhopalia is another sensory structure that some jellies possess. The rhopalia carry receptors that detect light, chemicals, and movement. Cubozoan jellyfish, for instance, have complex eyes with corneas, lenses, and retinas in their rhopalia. Even though these sea jellies respond to visual stimuli, scientists still can’t fathom how they interpret the images created by their eyes as they don’t have a brain that processes the images. However, a ring-shaped concentration of nerves (nerve ring) found in sea jellies seems to be involved.

Furthermore, a study conducted on the upside-down jellyfish, Cassiopea in 2017 shows that a brain is not needed to experience sleep. Cassiopea enters a sleep-like state at night where its pulse is less frequent than during the day. Also, it is slow to respond to disturbances during the night. The sea jelly appears to be tired the next day after being kept awake throughout the night. It is noticeable that their pulsing was slower than if they had a solid night of sleep. This was the first time an animal that doesn’t have a brain was observed sleeping. Therefore, this study and discovery suggest that sleep among all animals is an ancient feature with a shared evolutionary beginning, taking into consideration the neural network of sea jelly evolved prior to centralized nervous systems like a brain.

Do jellyfish have eyes?

The eyes of the majority of jellyfish are not concentrated in a single organ as humans own. Rather, their ability to see is aided by a network of nerves and proteins called opsins. Jellyfish do have eyes and their eyes don’t look like humans own except the box jellyfish.

However, their eyes are good enough to detect basic light signals. The light signals that look like a net are sent to the sea jelly’s rudimentary nervous system. Hence, researchers call it a nerve net. The slightly more complex jellies have a set of nerves; a nerve ring that borders the jellyfish’s bell. This nerve ring, therefore, is the closest thing to a central nervous system for a sea jelly. The light-sensing organ of the jellies lies within the rhopalia that are positioned at the edge of the umbrella-shaped bell.

There are structures within the rhopalia that help give balance to the jellyfish. The rhopalia are special as they have nerve nodes. These nerve nodes are concentrated and organized sets of neurons which is different from the dispersed nerve nets in the rest of their body.

The moon jellyfish and many other jellies from the class Scyphozoa have pretty rudimentary ocelli. It can detect nothing more than light and its intensity. The box jellyfish, on the other hand, leveled up to eyes that are much like humans and are complete with a lens, retina, and cornea. For instance,Tripedalia cystophora, a species of the box jellyfish has about 4 rhopalia. There are 6 eyes that lie within each rhopalium, giving a total of 24 eyes. Two eyes which are the upper and the lower lens eyes out of these six eyes have complex structures like human’s eyes, whereas the other 4 eyes are more primitive.

Therefore, the Tripedalia cystophora can actually see with these eyes as much as humans do, even though the vision might be a little blurry. The box jellyfish has been observed by scientists to use its sense of vision to identify habitats that it prefers, like among the roots of mangroves or to find prey. Some jellyfish varieties e.g the box jellyfish Carybdea sivickis with far more sophisticated nervous systems perform mating rituals characteristic of animals.

Opsins are responsible for the sight ability of both the moon jellyfish and the box jellyfish. The opsins are proteins that can detect light. These opsins in these animals are similar to the ones that allow humans to see the world around them. A series of complex biochemical changes occur when these opsins are hit by light, which finally leads to the activation of neurons. This is what allows jellies to respond appropriately to the light stimulus.

Sting of Jellyfish

Jellyfish stingers

The jellyfish stingers are on the tentacles. These tentacles possess microscopic barbed stingers and specialized cells called the nematocysts that it uses to capture its prey. Nematocysts are a type of specialized stinging cell that the jellyfish is armed with. They are organelles in these organisms which are within special cells called the cnidocytes and contain venom-bearing harpoons.

Due to touch or chemical cues, the cell is activated which causes the harpoon to shoot out of the cell and spear the prey. Each of the jellyfish stingers has a tiny bulb as well as a cold sharp-tipped tube that contains venom. As it pierces the prey, it releases toxins and this process doesn’t even take more than 700 nanoseconds. Once a sea jelly stings, thousands of very tiny stingers (nematocysts) are deposited in the skin. When inside the body, these stingers can continue to fire or release the jellyfish venom into the body.

Therefore, having contact with the tentacles of a sea jelly can trigger millions of nematocysts which pierce the skin and release venomous toxins. However, there are a few jelly species that are very toxic to humans e.g the Irukandji jellyfish (Carukia barnesi) and box jellyfish (Chironex fleckeri). These sea jelly species can cause severe reactions and lethal effects in humans. Once the tentacles of the jellyfish are touched, the tiny triggers on its surface release the stingers. Then, as the tube penetrates the skin it releases venom. Therefore, the immediate area of contact is affected and the venom may even enter the bloodstream.

Researchers in a study found a sea jelly species named Cassiopea xamachana. Once this animal is triggered, it will release tiny balls of cells that swim around it, thus, stinging everything in its path. This mechanism was described by researchers as self-propelling microscopic grenades and the jellyfish were named cassiosomes.

Jellyfish stinging mechanism

It’s the tentacles of a jellyfish that stings. The tentacles sting and release venom into their prey to paralyzes them. Generally, jellies don’t go after humans. However, a human can be stung by sea jelly when he/she swims up against one, touches, or even steps on a dead jellyfish.

How do jellyfish sting?

The jellyfish has specialized cells, cnidocytes that contain venom-bearing harpoons. Due to chemical cues or being touched, the cnidocytes of the jellies are activated which causes the harpoon to shoot out of the cell and pierce the prey.

Each of the sea jelly stingers has a tiny bulb as well as a cold sharp-tipped tube that contains venom. As it pierces the prey, it releases toxins and this stinging process doesn’t even take more than 700 nanoseconds. Once a jellyfish stings, it deposits thousands of very tiny stingers (nematocysts) in the skin. When inside the body, these stingers can continue to fire or release the jellyfish venom into the body. Therefore, having contact with the tentacles of a sea jelly can trigger millions of nematocysts which pierce the skin and release venomous toxins.

What does a jellyfish sting look like?

The sting from a Jellyfish stings has a distinctive appearance. They are usually diagnosed judging by appearance alone. However, they are mostly mistaken for stings from other sea creatures. The jellyfish sting looks like a mark along the skin. A print of the tentacle is left on the skin with brown, red, or purplish track marks along the skin. Usually, this physical marking is accompanied by the following:

  • Localized swelling
  • Itching
  • Burning, prickly, or stinging sensations
  • A throbbing pain radiating up a leg or arm
What does a jellyfish sting feel like?

Even though jellyfish stings are painful, the majority of the stings are not emergencies. When stung by a sea jelly the sting causes pain, red marks, itching, numbness, or tingling. A jellyfish sting feel is associated with itching, burning, or stinging sensations, and a throbbing pain radiating up the skin. Therefore, the feel of the jellyfish stings ranges from mild discomfort to extreme pain and death.

Also, stings from some kind of sea jellies such as the box jellyfish are very dangerous, and can even be lethal. The box jellyfish also called sea wasp is mostly found in the Philippines, Australia, Indian Ocean, and Central Pacific Ocean.

The stings from sea jellies can cause anaphylaxis. Anaphylaxis is a fatal form of shock that can result in death. In the Phillippines alone, a Jellyfish kill 20-40 people a year and the Spanish Red Cross in 2006 treated about 19,000 stung swimmers along the Costa Brava.

When dealing with box jellyfish, vinegar may be helpful but this is not applicable to the stings of the Portuguese man o’ war. Also, if vinegar is not available, some people believe saltwater may be helpful for a jellyfish sting. For a Physalia sting, immersing the sting in hot water can be the most effective way to reduce the pain.

However, it is not advisable to rub wounds from the jelly’s stings or use ammonia, alcohol, urine, or freshwater. This is because this can encourage the release of more venom. In order to reduce nematocyst firing, the area of jelly and tentacles is cleared. Also, many believe scraping the affected skin may remove remaining nematocysts which is wrong. Hydrocortisone cream can be applied locally once the skin has been cleaned of nematocysts to reduces pain and inflammation. Antihistamines may be used to control itching as well as immunobased antivenins for serious box jellyfish stings.

Jellyfish sting treatment

Once a sea jelly stings, it deposits thousands of very tiny stingers (nematocysts) in the skin. When inside the body, these stingers can continue to fire or release the jellyfish venom into the body. Hence, it is advisable to rinse the sting with vinegar.

The weak acid, vinegar might prevent the stingers from firing more venom into the body. As said earlier on, rinsing with cool fresh water is not advisable as it can make more stingers fire. Moreso, rinsing a sting with seawater was thought to prevent them from releasing more venom. However, recently, some experts are of the opinion that seawater can actually worsen a sea jelly sting. Likewise, it was recommended before to scrape off any stingers still in the skin. However, this is no longer advisable as it has been seen to make the stings worst.

Here is how to treat a jellyfish sting:
  • Remove the stung person from the water.
  • Rinse the stung area with vinegar. Hence, it is always advisable to always have a small plastic bottle of vinegar in your beach bag, in case of such emergencies.
  • Avoid rubbing the stung area as this can make things worse.
  • If possible, use tweezers to pluck away any tentacles still on the skin. Avoid scraping the area with any object, credit card, or other stiff cards.
  • Avoid applying ice or ice packs to a sting rather use a hot (but not scalding) shower or soak to help lessen pain.
  • Also, check in with your health care professional to see if pain relievers might help the person feel better.
  • However, call an ambulance immediately if someone has been stung and is exhibiting the following symptoms of jellyfish sting mentioned below:
Symptoms and signs of a jellyfish sting
  1. Having difficulty swallowing or breathing.
  2. Has a change in voice
  3. Feels generally unwell or has a bad pain
  4. Has a swollen lip or tongue
  5. Vomiting or nauseated
  6. Has a headache or is feeling dizzy
  7. Muscle spasms
  8. If the person has stings over a large part of the body
  9. Has a sting in the mouth or eye
  10. If the person may have been stung by a very dangerous jellyfish
How to prevent Jellyfish Stings

Most guarded beaches warn visitors about jellies. Hence, always look for a sign or warning flag about jellyfish. When there’s dangerous marine life in the water, you may see some beaches flying a purple warning flag. Look out for such a warning and be cautious.

When going to the beach, scuba diving, or skin diving always double-check to ensure you have a small container of vinegar and a pair of tweezers in your beach bag.

Jellyfish classification

Jellyfish classification
Sub phylum
Scyphozoa (True jellyfish)


Cubozoa (Box jellyfish)

Staurozoa (Stalked jellyfish)

In the class Scyphozoa, there are over 200 species of jellyfish and about 50 species of Staurozoa. The class Cubozoa has about 20 species of jellyfish. There are many jellyfish species in the Hydrozoa that do not produce medusae and about 1000–1500 species that produce medusae.

Jellyfish characteristics

  • Sea jellies throughout their lives transition between 2 different body forms; the medusa and polyp.
  • In jellyfishes, the medusa is the body plan that looks like an upside-down bell with tentacles hanging down from the inside.
  • The polyp of jellyfishes in the body plan is opposite to the medusa with the mouth and tentacles above, like a sea anemone.
  • Jellyfishes possess a unique stinging adaptation (nematocysts, or stinging cells) that is common to sea anemones and hydras.
  • Depending on the species, sea jellies vary greatly in size. Most of them range from 1cm (>1 inch) wide to about 40 cm (16 inches). The Lion’s mane jellyfish (Cyanea capillata) is the largest jellies that can be almost 1.8 m (6 feet) wide with tentacles over 15 m (49 ft) long.
  • Jellyfishes have two major cell layers: the internal gastrodermis and the external epidermis.
  • The gastrodermis of jellies lines the all-purpose gut and mouth whereby food enters and reproductive cells are released and taken in.
  • Jellies lack intestines and lungs. Thus, oxygen and nutrients enter in and out of the cell walls of jellies through the gastrodermis or even the outer cells of their bodies.
  • Jellies have outer cells that contain a loose network of nerves (a nerve net). The outer cells make up the epidermis. This forms the basic nervous system for jellies.
  • The bodies of sea jellies are made up of a gelatinous material (mesoglea) between the outer epidermis and the inner gastrodermis layers. The mesoglea of some small species can be very thin.
  • Jellyfishes are 95%  water and thus the mesoglea is made up of mostly water and some structural proteins, muscle cells, and nerve cells that form a kind of internal skeleton.

Types of Jellyfish

  • Scyphozoa
  • Hydrozoa
  • Cubozoa
  • Staurozoa

All jellyfishes are Cnidarian in the same phylum with jellies, sea anemones, and corals. Less than 4,000 out of more than 10,000 species of Cnidaria are Medusazoa. The medusazoa are the animals we call jellyfish. However, these 4,000 jellyfish can be divided into the four different types listed above.

Medusozoa is a subphylum that includes all cnidarians with a medusa stage in their life cycle. It includes the following major taxa:

Scyphozoa (True jellyfish or large jellyfish)

This type of jellyfish is the most familiar and includes the larger species. They are more colorful and interact with humans. Therefore, they are called true jellyfish. This group of Scyphozoa has at least 200 species and spends most of their lives in the medusa body form.

Scyphozoa have tetra-radial symmetry and a majority of them have tentacles around the outer margin of the umbrella-shaped bell. Also, they have long oral arms around their mouth in the center of the subumbrella.

Examples of Scyphozoa

  • Big red jellyfish
  • Moon jellyfish
  • Pacific sea nettle
  • Lion’s mane jellyfish
  • Helmet jellyfish
  • Nomura’s jellyfish
  • Cannonball jellyfish
  • Upside-down jellyfish
  • Compass jellyfish
  • Atolia jellyfish
  • Thimble jellyfish

Hydrozoa (Small jellyfish)

These types of jellies are jellyfish look-alikes and are not in the same group as the Scyphozoa. Compared to the true jellyfish, the swimming medusa stages of this group are usually small and inconspicuous. Moreso, the bottom-dwelling polyps, or hydroids of hydrozoa usually take the form of large colonies.

The medusae stage of Hydrozoa has tetra-radial symmetry. Always, they nearly have a velum attached inside their bell margin.  The vellum is a diaphragm used in swimming. These jellies do not have oral arms, though they have the manubrium which is a much smaller central stalk-like structure with a terminal mouth opening. Hydrozoa, therefore are distinct for the absence of cells in their mesoglea. They show a great diversity of lifestyle. Additionally, some of them maintain the polyp stage for their entire life and do not develop medusae at all e.g the hydra that is no longer considered a jellyfish. Also, a few of the hydrozoa are entirely medusal and have no polyp stage.

Amongst the hydrozoa is Siphonophores which are colonial hydrozoans. These hydrozoans don’t show alternation of generations, rather through a budding process, they reproduce asexually. The colonial siphonophores in the water column may be eye-catching. This group comprises the notorious Portuguese Man-o-Wars and several deep-sea life. Some of them stretch out like giant fishing nets up to 50 meters in length.

Colonial siphonophores are made up of many specialized individuals called zooids. These individuals all come from a single fertilized egg, thus, are genetically identical. Researchers discovered in 2016 what they believe to be a new hydrozoan species of Crossota, which was within the Mariana Trench and about 3,700 meters (12,140 ft) deep. This Crossota jellyfish is an exception to most hydrozoans. It floats in the water column like a glowing spaceship and spends most of its life as a large medusa. Generally, Hydrozoa has about 3,700 species.

Examples of Hydrozoa

  • Crystal jellyfish
  • Portuguese man o’ war
  • Clinging jellyfish
  • Blue button jellyfish
  • Immortal jellyfish

Cubozoa (Box jellyfish)

This group is the box jellyfishes, which are named so due to their box-like bells. They have a box-shaped bell and swim more quickly due to the velarium that assists them. Cubozoans may be more closely related to scyphozoan jellyfishes than to the Hydrozoa.

Some of the most potent venom known are produced by some cubozoans like the sea wasp (Chironex fleckeri). The Cubozoan possesses a more developed nervous system as well as complex eyes with lenses, corneas, and retinas compared to other jellyfish. Some of these jellyfishes (at least 36 species) even engage in elaborate courtship behavior.

Examples of Cubozoa

  • Sea wasp
  • Irukandji jellyfish
  • Tripedalia cystophora

Staurozoa (Stalked jellyfish)

This group consists of the stalked jellyfishes. Unlike other jellies, they don’t float through the water rather they live attached to seaweed or rocks. These jellies mostly inhabit cold water and are trumpet-shaped. They are distinct for their beauty and camouflage combination. These animals are found globally in oceans and there are about 50 staurozoan species inhabiting shallow and deep water, with a few that can be seen in freshwater.

Stalked jellyfishes are distinguished by a medusa form that is generally sessile and oriented upside down. Also, they have a stalk that emerges from the apex of the bell (calyx) that attaches to the substrate. However, some Staurozoa also has a polyp form that takes turns with the medusoid stage of the life cycle. Initially, Staurozoa were classified within the Scyphozoa but recently they’re no longer classified as such.

Examples of Staurozoa

  • Haliclystus auricula
  • Haliclystus antarcticus

Species of Jellyfish

  • Flower Hat jellyfish
  • Cauliflower jellyfish
  • Mangrove box jelly
  • Crystal jellyfish
  • White-spotted jellyfish
  • Upside-down jellyfish
  • Black sea nettle jellyfish
  • Fried egg jellyfish
  • Lion’s mane jellyfish
  • Atolla jellyfish
  • Narcomedusae
  • Bloody belly comb jellyfish
  • Pink meanie jellyfish
  • Moon jellyfish (also known as Common jellyfish, Aurita, or Saucer jelly)
  • Australian Box jellyfish
  • Velella
  • Mushroom cap jellyfish
  • Compass jellyfish
  • Many-ribbed jellyfish
  • Flame jellyfish
  • Barrel jellyfish
  • Mauve singer
  • Cigar jellyfish
  • Nomad jellyfish
  • Chironex fleckeri Box jellyfish
  • Carukia Barnesi

Crystal Jellyfish

The crystal jellyfish as its name implies is completely colorless. It is usually found in the waters around North America’s coast. They have about 150 tentacles that line their glass-like bell and look crystal clear in the daylight. Crystal jellies are described as brightly luminescent jellies. They have glowing points around the margin of their umbrella-shaped bell.

The components that result in bioluminescence include aequorin and GFP. Aequorin is a calcium-activated photoprotein that emits blue-green light. The accessory GFP (green fluorescent protein), however, accepts energy from the aequorin and re-emits it as a green light.

Cauliflower Jellyfish

This sea jelly has wart-like projections on its bell which makes it resemble a vegetable. That is how the jellyfish got its name and it is also called the crown jellyfish. It is a beautiful species of jellyfish that is commonly found within the waters of the mid-Pacific to the Indo-Pacific. Also, sometimes it is found around the Atlantic Ocean off of the West African coast.

The Cauliflower jelly is one of the most venomous jellyfish species that are harmless to humans, thus, no painful sting from them. They grow relatively large in size and can reach up to 1.5-1.9 ft in diameter. This sea jelly has 30 filaments with stinging cells that stick out from their bell. In Japan and China, this animal is considered to be a delicacy and is used also for medicinal purposes in these areas.

White-spotted Jellyfish

These jellies have very mild venom, hence, any stings from their stinging cells are harmless to humans. Generally, they don’t even use their venom at all to catch food. However, as filter feeders, they can filter over 50 cubic meters of ocean water every day. Thereby a swarm or bloom of these animals can clear an area of zooplankton and cause a shortage for the fish and other marine life that also feed on these zooplanktonic marine lives.

In some areas, the white-spotted jelly is considered to be an invasive species. This is because, their hungry appetite in areas like the Caribbean Sea, the Gulf of California, and the Gulf of Mexico, cause somewhat of a problem for the native species ranging from shrimps to corals.

The White-spotted jellies (Phyllorhiza punctata), for instance, live in the western Pacific, from Australia to Japan, and as filter feeders, they can sift through more than 13,000 gallons of water a day for zooplankton. These jellies are known for their speckled crowns. Therefore, their presence can clear an area of zooplankton, leaving none for the fish and crustaceans that also feed on zooplankton.

Black Sea Nettle Jellyfish

The Black Sea Nettles jellyfish is one of the largest jellyfish. This sea jelly can be found in the deep sea Pacific waters around Southern California and are not that common to a lot of ocean waters. Their bells’ diameter can reach up to three feet with their long tentacles that reach up to 20 feet in length. The stinging tentacles of these jellies are about 25 feet long.

Despite these species being called a Black Sea Nettle, their bell is only black on the mature jellies, whereas the bell of the small and immature jellies is reddish to maroon color. The tentacles of these large and small jellies are whitish-pink with oral arms of reddish-pink. Hence,  like several other deep-sea dwellers, they are actually red in color and this color makes it easier for them to blend in with the dark water.

These jellyfishes are relatively new to science, thus, much about them is not actually known. This is partly a result of these species being very difficult to raise in captivity as well as them not usually discovered in the wild.

Fried Egg Jellyfish

This sea jelly (Cotylorhiza tuberculata) got its name from its resemblance to an egg yolk. The jellyfish has a yellow bell that is surrounded by a lighter ring with mouth-arms that are truncated. Rather, there are longer projections with disklike ends that make it look like a dome dotted with white and purple pebbles.

The Fried Egg Jelly is also called the Mediterranean jellyfish and is one of the jellies that have venom but are harmless to humans. Actually, its sting is so mild that small fishes sometimes use its tentacles to provide shelter in the open ocean water.

Usually, when looking at these animals, it is common to see tiny fish hiding inside the tentacles of the animal for their own protection. Also, smaller crab species sometimes will hitch a ride on the bell of these animals. These jellies can be found inhabiting the Aegean Sea,  Atlantic Ocean, and the Mediterranean. In fact, these Mediterranean jellyfishes only survive for around 6 months. Usually from the summer months to the winter and dies once the water and weather start to cool down.

Flower Hat Jellyfish

These sea jellies are native to the Western Pacific and are usually found off the Southern Japan coast as well as within the waters of Brazil and Argentina. Mostly, they seem to hang among seagrass near the ocean floor instead of pulsing their way through the open waters. They hang around the seagrass because of the small fish they prey on.

These jellies are beautiful with extraordinary colors of their bells. However, despite their beauty and attractiveness, their stings are very painful and leave a bright burn that resembles a rash. As a result, blooms of these jellies make swimming in coastal waters off Argentina hazardous. Therefore, the swarms of these jellies in Brazil interfere with shrimp fishing because they clog the nets and drive shrimp away probably to deeper water.

Atolla Jellyfish

The Atolla Jellyfish is also known as the Coronate Medusa jelly. They can be found globally and a majority of deep sea-dwelling Atolla has super awesome bioluminescent abilities.

This jelly species use their bioluminescence to avoid predators, unlike most of the deep-sea ocean dwellers that use theirs to attract prey. Once a predator attacks the Atolla, it creates a series of flashes that resembles an emergency siren. These flashes that they produce draws in more predators that will be more interested in the original attacker, instead of the Atolla. Thus, the Atolla jelly gets a chance to make an escape. It is this defense mechanism that has given it the nickname the alarm jellyfish deep-sea species.


These jellies sometimes shortened to narcos are an unusual type and have two stomach pouches compared to the different species of jellyfish. The Narcomedusae when swimming,  holds its long tentacles out in front of it in order to fill both pouches with prey. According to researchers, this makes them a more effective ambush predator.

Some species of Narcomedusae, instead of laying the normal jellyfish eggs can even grow inside their own mother. Hence, providing nourishment and a safe environment for her young. The babies of the Narcomedusae can then leave their mother, in search of another jelly that is of an entirely different species. It then attaches to the jelly’s flesh and flourishes on the nourishment and safe environment it provides.

Pink Meanie Jellyfish

This jelly is one of the largest jellyfish which have only been first observed in large groups in the year 2000 off of the Gulf of Mexico. They happen to be the first new family of jelly species identified since 1921.

The Pink Meanie preys on and has a taste for other jellies.  It uses its very long tentacles to entangle the jellies, reeling them in and consuming them. Their tentacles could be up to 70 feet and these jellies are known to eat as many as 34 jellies at a time.

The Pink Meanie can be found in the US Atlantic, the Coastal Caribbean, and the Gulf of Mexico, and probably other parts of the world as well. It is also called Drymonema Larsoni which is named after Ronald Larson, a U.S. Fish, and Wildlife scientist. Back in the early ’80s, Ronald Larson pioneered work on the Pink Meanie.

Mangrove Box Jelly

One of the smallest jellies in the sea is the mangrove box jelly. It is said to grow to be only the size of a grape. However, they are unique for their cube-shaped medusa, which is a notable deviation from the familiar medusa dome of most jellies. The mangrove box jellies, therefore, move more rapidly due to the distinct squareness of their medusa.

Upside-Down Jellyfish

The upside-down jellyfish (Cassiopea) as its name implies normally rests its bell on the surface of the seafloor and swims with its stubby oral arms towards the sky. The mutualistic relationship this jelly has with dinoflagellates is the reason it swims upside down. It swims in that manner in order to expose the symbiotic dinoflagellates that live in its tissues to the sun. Therefore, this allows the dinoflagellates to photosynthesize. These upside-down jellies are usually found in warm water, like in the water around the Caribbean and Florida.

Lion’s Mane Jellyfish

The largest known jellyfish species as well as the most dangerous happens to be the lion’s mane jellyfish (Cyanea capillata). This jelly can grow up to six and a half feet long and usually, its average length is 1 and 1/2 feet.

They possess a mane that contains hundreds and sometimes even more than a thousand tentacles that divides into eight clusters. This sea jelly is sometimes called the Arctic red jellyfish or the hair jelly and they inhabit the boreal waters of the Arctic, northern Pacific Oceans, and northern Atlantic.

The lifespan of a Jellyfish

Most jellyfish don’t live for long. Based on their species, the Medusa or adult jelly is usually short-lived for a few months whereas the polyps can live and reproduce asexually for many years or decades. However, some species in captivity can live for 2-3 years.

Interestingly, there are only one jellyfish species that is almost immortal. The Turritopsis nutricula, a small hydrozoan, after reaching the adult medusa stage has the ability to revert back to the polyp stage through a process called transdifferentiation. It is the only animal known to have such ability.


The vast aggregations of jellyfish are known as jellyfish blooms or jellyfish outbreaks which causes several problems.

Too many jellyfishes in a water body result in jellyfish bloom

Listed below are some of the wide array of problems the bloom may cause:

  • When there are too many jellies in the water, it can be dangerous to swimmers, and this results in some towns closing their beaches.
  • At coastal power plants, jellies have clogged up machinery and cause power outages.
  • Also, they can interfere with fisheries because as they feed on fish larvae, they reduce the fish population. Therefore, fishermen end up catching jellies instead of the fish they are fishing for.
  • Jellyfish blooms can change seawater chemistry.

Causes of Jellyfish bloom

  • Overfishing
  • Nutrient pollution
  • Climate change
  • Submarine Sprawl


As a result of overfishing, between 100-120 million tons of marine life on an average each year have been harvested from the ocean over the past two decades. Many of these aquatic species such as fish and invertebrates like squid and octopus feed on the same kind of organisms that the jellies feed on. These jellies end up having less competition for food as other aquatic organisms are over-fished from the sea. Therefore, as a result of less competition for food, they grow well and reproduce with fewer limits, Hence, resulting in bloom.

Nutrient pollution

There is usually nutrient pollution in water bodies when fertilizer runoffs enter water bodies leading to eutrophication where phytoplankton like algae blooms and create dead zones in the water that no longer support life. Phytoplankton grows very quickly due to the nitrogen and phosphorus in fertilizer. Once there are so many of these organisms in the water, oxygen is depleted from the water. Even though most animals can’t survive in such oxygen-depleted conditions, many jellies can tolerate low-oxygen environments. Therefore, nutrient pollution in water bodies causes jellies to bloom.

Climate change

The ocean warming up due to climate change might cause a jelly bloom. This is because the warmer water could facilitate embryos and larvae of jelly to develop more quickly. Thereby, allowing their populations to increase rapidly as jellies that prefer warmer water will have more habitat to inhabit. However, this also affects some cold-water jelly species as their own habitat shrinks.

Submarine Sprawl

Many industries build structures that serve as nurseries for jellyfishes. e.g docks, oil platforms, and ocean sprawl. Such industries include drilling, shipping, and aquaculture.

This ocean sprawl ends up providing suitable habitat for jellyfishes to complete their lifecycle and reproduce. Jellies during their polyp stage require solid surfaces to settle upon rather than sand. Therefore, it’s much easier for them to attach to man-made structures like the ocean sprawl.


Below is a video you can watch for more explanation on jellyfishes.