Jellyfish or Sea Jellies Upside down jelly Cassiopea andromeda

Jellyfish or Sea Jellies which is correct ?

Jellyfish or Sea Jellies An upside down jelly Cassiopea andromeda photographed in Ushaks Marine World
Despite the name, Sea Jellies – Jellyfish are not fish and the term is not scientifically appropriate. Many scientists are beginning to refer to them as jellies or sea jellies in a similar fashion to the name change occurring with starfish into sea stars, which is a more accurate description.

There are a large number of organisms with similar characteristics to jellies, but jellies as we traditionally know them are in the phylum Cnidaria and the class Scyphozoa. They have various stages in their life cycle and what we think of as jellies are actually jellies in the medusa stage of their life cycle, also described as the non polyp form.

Jellyfish or sea jellies have been around in their present form for at least five hundred million years but possibly a lot longer, making them the oldest multi organ animal that we know of at present.

Jellyfish or Sea Jellies A moon jellyfish Aurelia aurita photographed in Ushaka Marine World


Jellyfish or sea jellies range in size from about 1 mm to 2 meters in width in the medusa or non polyp stage. The lions mane jellyfish has tentacles up to 36.5 meters long and the Nomura’s jellyfish can reach up to 2 meters in bell circumference and weigh over two hundred kilograms. They also have a wide range of colors that they come in, often influenced by their diet. Some jellies are transparent while others are white, blue, green, brown, orange or red.

Jellyfish or Sea Jellies Purple-striped Jellyfish, Pelagia panopyra

Jellyfish or sea jellies are essentially free swimming marine animals that have an umbrella shaped bell filled with gelatinous matter and trailing tentacles.  The bell can pulsate for locomotion and often has a skirt on it for improved hydrodynamics.  They have stinging tentacles for defense and the capture of prey.

crowned jellyfish


They do not have what we would traditionally call a brain or centralized concentration of nerve cells. Instead they have a nerve net distributed throughout the body which has various simple sensors on it and operates in a decentralized fashion. Information is transmitted through the net and via a circular net that runs around the bell with rhopalia on it, small structures containing sensors to sense light and gravity. The circular net around the bell also controls the contraction of the bell for propulsion. Jellies use their light sensing cells to orientate themselves against the light.

Jellyfish or Sea Jellies Purple-striped Jellyfish, Pelagia panopyra


They use pulsations of their bell to propel themselves forward and having no sight, have limited control over where they will end up, their directional logic being generally limited to either moving away from light or towards it. New evidence suggests that they have the ability to sense a current and swim into it.


The gelatinous matter known as mesoglea consists of a jelly like substance surrounded by two layers of skin. The ectoderm and the endoderm which contains muscle bundles and nerve paths. It serves as a hydrostatic skeleton and allows the jelly to keep its shape in the water.

The manubrium hangs down from the bell, often surrounded by oral arms and it connects with the single aperture which functions both as a mouth and an anus. This opens into the gastovascular cavity which is where digestion takes place and nutrients are absorbed. It is joined to the radial canals which extend to the bell where the tentacles are attached. Because their skin is so thin they do not require a respiratory system and the body is oxygenated by diffusion from the water.

 Purple-striped Jellyfish, Pelagia panopyra


The tentacles which come off the edge of the bell have large numbers of nematocysts or stinging cells on them. These are similar to a tube that has been pulled inside out into its self with a sharp point and has a mechanism to pump poison through the end of the point. They are extremely small, about 0.001 mm in diameter. There is a trigger on the exterior of the tentacle and when this trigger is activated either chemically or physically the tube or tubule as it is known inverts its self. Pushing outwards and pushing the point into the prey and it then pumps poison up the tubule into the prey. This process of firing takes place in 700 nano seconds which is extremely fast and occurs with substantial pressure. In some species the point is able to penetrate the shell of small crustaceans.

There are two types of stinging cells in jellies tentacles , nematocysts and spirocysts and these inject hypnotoxin, thalaxin and congestin into the prey. Hypnotoxin has an anaesthetic effect and paralyzes the prey. Thalaxin has an allergenic action, generating an inflammatory reaction. Congestin paralyzes the circulatory and respiratory systems of the prey. Some jellies such as the moon jelly are completely harmless to humans and research has shown that jellies with longer tubercles that are able to penetrate human skin into the soft tissue are more dangerous to humans. Those with shorter tubercles such as the moon jelly are generally  harmless.

Jellyfish or Sea Jellies A spotted jelly photographed off the coast of mafia island tanzania


Jellyfish or sea jellies are found in every ocean in the world from the surface to the deeps, members of the Scyphozoa class are exclusively marine and are common in coastal areas.

Jellyfish or Sea Jellies Purple-striped Jellyfish, Pelagia panopyra


Jellyfish or sea jellies have a wide range of food, some such as the upside down jelly Cassiopeia andromeda, rely on a symbiotic relationship with algae to produce a lot of their food. Most jellies will catch food with their tentacles ranging from small plankton to large fishes and even other jellies. Once the tentacle has trapped prey it then retracts bringing the prey up to the stomach.

Among their predators are Sunfish and loggerhead turtles.

Jellyfish or Sea Jellies Blue blubber Jellyfish photographed at Ushaka marine world


Jellyfish or sea jellies reproduce through both sexual and asexual reproduction. During the Medusa stage specialized organs known as gonads form either eggs or sperm and in some species, female jellies release eggs into the water table and these are fertilized by sperm released by the males. In others the eggs are fertilized in the stomach of the female when the sperm released by the males swims into the females stomach and then fertilize them there.

Some jellies such as the moon jelly have special areas on the oral arms which function as brood chambers. The eggs hatch into larvae known as planula with cilia on them allowing them to swim and these attach themselves onto a firm substrate and develop into polyps called scyphistomae.   These polyps produce numbers of ephyra, that detach and swim off to grow into the medusa stage. The polyps can also bud asexually producing other polyps.

Jellyfish or Sea Jellies A young spotted jelly photographed off the coast of mafia island tanzania


Blooms of jellyfish or sea jellies occur when the conditions for breeding are ideal. Usually associated with warm weather and an abundance of food. Some blooms occur seasonally when the conditions are just right for a species of jellies in a given area. It is suspected that the polyps when attached to the ocean floor wait for ideal conditions. When these occur they release large numbers of ephyra into the water which grow into mature jellies, resulting in a very rapid increase in population numbers.

Swarms of Nomad jellyfish in the ocean off Dar es Salaam Tanzania 2016

The effects of a bloom of jellyfish or sea jellies can be devastating particularly for small communities who rely on fishing for their subsistence. When their nets are full of jellies instead of fish they have no or little food. For the last few years the Japanese fishing industry has been decimated at certain times of the year by massive blooms of large jellies called Nomuras.

They weigh up to 220 kilograms each. Power stations have been forced to shut down after their cooling systems have been blocked by jellies and offshore fish farms have been devastated.  The effects of global warming on jelly numbers are unknown as such. However with the removal of their predators through over fishing, pollution and development the consequences are likely that the jelly populations worldwide will grow.

Jellyfish or Sea Jellies Fishermen with their nets full of blue jellyfish after a bloom of bluejellyfish on mafia island tanzania


Concentrations of jellyfish or sea jellies tend to be seasonal and whether there are large numbers in an area is often determined by warm weather conditions. Local knowledge is essential because various species tend to be found in known areas and particularly in warmer areas it is best to stick to  swimming beaches with lifeguards who monitor the local conditions. Some jellies such as the nomad jellyfish have entered the Mediterranean and have become a threat on tourist beaches all the way across to Malta. Others have entered the Black sea, but in any given area the local people will tend to know the local species and how to deal with them.


You can get stung on the beach, even when the tentacles have broken off the body, they still have the ability to sting for a long period of time and pieces are often washed up on the beach. If you have a small puppy and you are walking them along the tide line on the beach where everything is washed up please take care because a puppy may sniff and touch the tentacles and they will probably sting it on the nose. It will probably not be fatal but you will have a very unhappy puppy.

There is the old story of the holiday maker coming down to the beach and seeing a jelly lying there and putting it on his head and being stung to death. Probably the story is not true, but if you see a jellyfish on the beach do not touch its tentacles.

Jellyfish or Sea Jellies Blue jellyfish washed up on the beach after a bloom in the Mafia island channel tanzania

Most swimming beaches will issue warnings about jellyfish or sea jellies in the water and it is wise to heed these warnings. Jellyfish or sea jellies swimming below the surface of the water are very difficult to spot. Even if you are on the lookout for them, you often find them first by being stung. If there are jellyfish or sea jellies in the water it is sensible to get out. It is particularly important to get children out the water quickly if there are any jellies in the vicinity.

If I am diving or swimming in an area where there are likely to be jellyfish or sea jellies I wear a full lycra suit which provides protection against jelly stings. If it is really bad I will wear a hood as well. Even though the suit is thin it seems to prevent the nematocysts from firing which implies a chemical element in the firing mechanism, although most experts seem to disagree on this believing that it is a physical trigger. It is rumored that some Australians often wear pantyhose when swimming in waters with jellies in them for the same  reason.


Most Jellyfish or Sea Jellies have stings that are only mildly irritating and do not hurt much at all. If it is just a very mild sting I tend to just leave the sting alone or wash it through the water to get the tentacle off. If it is a worse sting you very quickly know about it. The worst jelly that has stung me is a nomad jelly, its tentacles bumped into my leg which felt as though it had been branded by a hot iron. The pain is burning and fairly extreme for about ten or fifteen minutes and it took three weeks for the rash and blisters that developed to go away. Essentially the toxins in the nematocysts provoke an acute inflammatory response with swelling and sometimes blisters. You can also develop a rash in the area that has been stung.

Nomad Jellyfish sting


The first thing to do is head for the shore because you do not want to be stung again and there may be a  possibility you will have an allergic reaction to the venom.


The second thing that you need to ideally do simultaneously while heading out the water is to get the tentacles off of you. They carry on stinging you and pumping poison into you. Having been stung so many times the minute I feel the sting, I immediately start getting it off me. If I am in deep water I will use my hand as a paddle to push water at the area that has been stung and float the tentacles and any mucus off of me. If I am in shallower water  I will aggressively splash the area with seawater.

The quicker you get all of it off you the better and it makes a massive difference in terms of the pain. Its best not to touch it with your hands and rather than running around looking for tweezers and sticks I splash or wash it off  through fast movements in the water. If there is a handy rock pool nearby so much the better to get it all off by rinsing it and splashing seawater onto the sting site to get the smaller tubules you cannot see off. Getting it off very fast is highly recommended.


Once you have the main part of the tentacles off you, it is important to understand that you still have large quantities of the minute stinging cells tubules (0.001 mm in diameter)  attached to you. You cannot see them as they are so small and there is still poison in the tubules. After thoroughly splashing the site, if you can find something suitable with a sharp edge such as a shell, knife edge or a credit card, lightly scraping this across the area will remove more of the tubules. There will be a lot less poison that could go into you. These early steps can save you a lot of pain.

You can run for the nearest shower on the beach and wash it off, which is what most people do but be warned that fresh water causes the stinging cells to release more venom. As the tentacle goes down you it will continue stinging you. It is highly recommended to wash the tentacle off with salt water for this reason.

Some people recommend using a handful of sand to rub the tentacle off. Quite why you would want to sand paper the sting into your skin is beyond me. This sounds like a silly idea and it is. If necessary use a shell or stick or anything sharpish that is handy to scrape it off.


If you have allergies or have been stung around the neck and there is any swelling then get to the nearest Lifeguards hut or Doctor very quickly. If you have quite a few stings then it is also a good idea to get to a Doctor.


Just in case its best to be safe and get yourself to a doctor if there is swelling around the lips and eyes, rapid development of a rash, chest tightness, shortness of breath or wheezing, severe dizziness or faints, persistent sneezing or coughing, hoarse voice, difficulty swallowing or throat tightness or any signs of shock (pale skin, rapid pulse or fainting). Fatalities have occurred but only very very rarely and you would have to be extremely unlucky for it to get that bad.


Poisons work on body mass, so the smaller you are the greater the effect of a given amount of poison. Children, asthmatics and those with allergies are most at risk and need to be watched carefully if stung.


It is important to stay calm and there are quite a few options to relieve the pain. It seldom hurts much for more than twenty minutes before it starts itching. You can take a paracetemol tablet to help with the pain.


New research seems to show that a lot of the old remedies do not work that well. Lets run through the options.

On the herbal side as a child growing up on the coast in Natal I was taught by my grandfather to use the leaves of the Carpobrotus deliciosus plant or the related species which all resemble each other. Where this remedy originates from no one is sure. They are known as the sour fig, vygie or umgongozi in Natal and unless you are in an urbanized area such as a big city, on a South African beach you can almost always find this plant somewhere nearby on the dunes of a beach. It is very distinctive and has triangular succulent leaves and purple flowers in Natal but in the Cape the related species have yellow or white flowers. They all work on the jellyfish or sea jelly stings.

Jellyfish or Sea Jellies herbal remedy for jellyfish or sea jelly stings Carpobrotus deliciosus plant

I was taught that the more red the leaf the better it works. Usually though when you need them in a hurry you cannot find the red leaves and just use the nearest green ones. You simply break them off and rub and squeeze the juice on the sting. It does provide relief from  personal experience but so far there is no science behind the remedy. For what its worth this plant has been taken to California in the USA for stabilizing dunes and Australia for the same purpose, where it is known as pig face.


Vinegar is a common suggestion and research indicates that it does work so if you have any handy pour it liberally on the sting and then hold a cloth soaked in vinegar on the sting. What the acetic acid in vinegar will prevent the tubercles from pumping more venom into you.

Alcohol or mentholated spirits is not recommended by anyone.

Scrub’s Ammonia used to be used by all the lifeguards in Durban in South Africa in holiday season and appeared to work on the holiday makers.

Meat Tenderizers such as Aromat or paw paw juice, some people swear by these but personally I have never tried them and there appears to be no science behind how they could work. Supposedly a water mixture with powder type meat tenderizers is the way to go.

Urine is commonly suggested as a cure and there is a bit of hit and miss in whether it will work. There is uric acid in some pee but not in other. The acid appears to be the active ingredient which breaks up the poisons. Try at your own risk and bear in mind people may never talk to you again if you urinate on them.


All the research done in Australia where people get stung a lot by jellyfish or sea jellies, seems to indicate that soaking in hot water  is the best cure. This because it breaks the poison’s protein chains up. They recommend soaking between 42 C and 45 C or in other words just about as hot as you can take it for 20 minutes. Most geysers are set between 55 C and 65 C to give you an idea of what really hot is. Be careful not to burn yourself and a hot shower should help if there is nothing else.

Anything a bit above body temperature is likely to give you some pain relief according to the research. Of course there isn’t much hot water on normal beaches. What you can do as a precaution especially if you have kids is take a thermos flask of hot water to the beach with you.

If there is no hot water nearby then it is recommended that you use ice or something cold, on most beaches  you can find a cold cool drink somewhere to push on the sting on route to finding some hot water.

A standard antihistamine antiseptic cream can be used on the sting site to reduce itching and prevent any infection.


Jellyfish or Sea Jellies fall in the phylum Cnidaria and what we traditionally call jellies, which are sometimes refered to as the true jellies are in the class Scyphozoa. They have several stages in their life cycle from fertilized egg to polyp to the medusa stage which is what we commonly think of when we think of a jelly.


The class Cubozoa contains the box jellies, some of which have deadly poisons and are as their name suggests jellies, but they are box shaped. They have a more developed nervous system than traditional jellyfish and have much more complex eyes with lenses, corneas and retinas in some species.


The class Hydozoa contains such species as Velella Velalla, fire corals, siphonophores such as the bluebottle, hydra and the freshwater jelly and the hydroid jelly and others which are not regarded as true jellies.

Solitary Hydroid


The class Staurozoa contains stalked jellies which do not swim and spend their lives permanently attached to a substrate.


Then we have the comb jellies which are in the Phylum Ctenophora and are unrelated to what we traditionally think of as jellies, they are also composed of gelatinous matter and have rows of cilia down the side which they use for swimming. They do not sting.

Comb Jelly


There are also selps in the phylum Chordata  sub phylum tunicata which are also composed of gelatinous matter. These do not resemble jellies and are often composed of long chains as can be seen below.

Leucothea species Salp

Traditional jellies

Kingdom: Animalia
Phylum: Cnidaria
Subphylum: Medusozoa

Scyphozoa Traditional Jellies
Cubozoa    Box Jellies
Hydozoa   Fire Corals, Hydra, Siphonophores
Staurozoa   Jellies that do not swim and are permanently attached to a substrate
Comb Jellies>
Phylum: Ctenophora


Kingdom: Animalia
Phylum: Chordata
Subphylum: Tunicata
Class: Thaliacea
Order: Salpida
Family: Salpidae


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Canon 7D