Jellyfish Identification Guide (Types & Fun Facts)
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The jellyfish has a bit of a bad reputation, largely because many species can deliver a painful, and sometimes fatal sting to humans. But this is simply a means of protecting themselves and just one of the wonderful ways that nature allows these fascinating creatures to thrive.
Once you get over the initial fear of jellyfish, you’ll soon see that these marine animals are interesting, beautiful, and one of the most unique creatures on the planet. Shall we get to know them a bit better?
Jellyfish Overview
What exactly are jellyfish? Well, they aren’t a type of fish, despite what their name might have you believe. In fact, jellyfish are actually a type of invertebrate and are members of the phylum Cnidaria which belongs to the same family of creatures as coral and sea anemones.
It is believed that there are around 2000 species of jellyfish, and they are found all over the world. However, it’s also reported that there are hundreds of thousands more species yet to be discovered.
Scientists believe that jellies have been gracing the planet for the last 500 million years; predating even the dinosaurs. They’re certainly one of the most primitive creatures we see today, and they are usually found in saline waters, although there are a few species that inhabit freshwater.
Jellyfish start their lives as small polyps and then develop into what is called a medusa. This is the gelatinous, bell-like animal that we are used to seeing in the ocean.
Among the medusas, there are four main groups.
- Scyphozoa (true jellyfish) – there are around 200 jellies within the scyphozoa category which is made up of cup-shaped jellyfish that usually grow to no more than 15 inches (38 cm), although there are exceptions.
- Cubozoa – this includes jellyfish that have a box-shaped body. There are currently around 51 known species of the colloquially known box jellies
- Hydrozoa – a whopping 3200 species of hydrozoa have been discovered up until now and are not considered true jellyfish. One of the most well-known examples of these is the Portuguese man o’ war (Physalia physalis).
- Staurozoa – these are stalk-like creatures whose medusas usually exist upside down with an appendage coming out of the body. There are only around 50 species of staurozoa.
Jellyfish Anatomy
Jellyfish are quite unlike any other animal on the planet and have a very unique physical makeup. Despite being called jellyfish, they’re not actually made from jelly, at least not in the sense that we would think.
They are made up of three layers of gelatinous skin, but this accounts for only 5% of the animal since the other 95% of a jellyfish is water! They come in a range of colors; some are totally see-through and very difficult to see, while others have bright colors and beautiful patterns. In terms of size, jellies are very diverse, with some growing to several feet, whereas others are just a couple of inches in diameter.
Jellies have what is known as a hydrostatic skeleton, and this is made up of those three layers we talked about and water. This flexible skeleton is supported by fluid which helps it to retain its shape.
What’s very interesting about the jellyfish is that it doesn’t have any internal organs. They absorb oxygen through their skin and even eat and poop through the same opening, so there’s no need for a complex digestive system either. On top of this, they have no brain, no heart, and no bones; we told you they were unique!
If they have no brain then how do they function? Well, our gelatinous friends have something called a nerve net that allows them to sense their environment; no need for a brain!
A lot of jellyfish move through the water on ocean currents. However, there are some that are able to propel themselves. They usually do this by contracting and relaxing a muscle around the edge of the bell which draws in water. When relaxed, the water is released and moves the animal forwards.
More than 50% of jellyfish species are bioluminescent. This means that they are able to create their own light and they use this for various reasons such as attracting prey, as a warning to predators, and as illumination for species that live in deeper water.
What do Jellyfish Eat & How Do they Consume their Prey?
Jellyfish might seem like simple creatures, but they are very effective at catching their prey. They use their tentacles to catch and stun their prey. There are cells called nematocysts that are attached to the jellyfish and deliver a toxic sting to their victim. The jelly is then able to move the food up to its mouth using those same tentacles.
The diet of jellyfish may vary slightly by species, but these creatures largely feed on plankton, small fish, crustaceans, and occasionally, other jellies. They certainly aren’t fussy eaters, and fisheries have complained that they take up so much of the available food in certain areas that there’s hardly anything left for the fish.
In the gastrovascular cavity, there is something called the gastrodermis which lines the cavity and absorbs all of the nutrients from anything the jellyfish eats. When it is done, any excrement comes back out of the mouth hole which serves a dual purpose.
Jellyfish Reproduction & Lifecycle
Much like everything else about the jellyfish, the way they reproduce is anything but usual. They begin their life as a fertilized egg which eventually hatches into a larva. This larva then floats down to the bottom of the water and attaches itself to a rock. At this point, it is called a polyp. Over time, that polyp becomes a mature jellyfish which is known as a medusa; these are the bell-shaped animals we are all familiar with.
But how do jellyfish go about reproducing? Amazingly, these creatures are able to produce both sexually and asexually, and as such, each jelly has a dual body form. Most of the time, the jellyfish will release eggs and sperm into the water for outward fertilization. However, there are some instances that sperm will be released and enter into the mouth, fertilizing the egg inside the animal. Both eggs and sperm are released from the mouth; which also serves as the opening to eat and excrete!
Do Jellyfish Have Predators?
You would think that, because jellyfish have a nasty sting, no other animal would be interested in eating them. But that is not true. There are plenty of jellyfish predators, and they aren’t in the slightest bit affected by their sting.
There are around 150 species of animals that are known to eat jellyfish and these include crustaceans, fish, turtles, and even other jellyfish. Two of the most notable predators of the jellyfish are the sunfish and the leatherback turtle.
We also have to keep in mind that humans eat jellyfish, and we can see that we’ve hunted them for as long as 17 centuries!
How do Jellyfish Sting?
Jellyfish have tiny cells within their tentacles known as nematocysts or cnidocytes. These release a harpoon-like structure upon contact and it is this that pierces the skin of the prey before the toxins are released.
For humans, one of the main issues is that the tentacles will often stay stuck to the skin or even clothing and can carry on stinging until they are removed.
Types of Jellyfish
While there are only 2000 species of jellyfish that are currently known to humans, it is thought by scientists that there could be as many as 300,000 undiscovered species! How amazing!
But while we don’t have the capacity to talk about all of these thousands of jellies, let’s get better acquainted with some of the most fascinating things on the planet.
1. Common Jellyfish (Aurelia aurita)
Also known as the moon jellyfish, the common jelly is the least dangerous species to humans. While it does sting, its venom is unlikely to do much more than cause localized pain.
The common jellyfish can be found in the Pacific, Atlantic, and Indian oceans and prefers to frequent coastal waters. Here, it swims using its bell to propel itself close to the surface. This is so that the tentacles can get a greater spread under the water for catching prey; the main menu item for these jellies is zooplankton.
Moon jellyfish usually have either a streaked or spotted appearance and can grow to anywhere between 2 inches (5 cm) and 16 inches (40.6 cm). They begin their lives as polyps that attach to a rock before maturing into what is known as a medusa. Usually, they live for between 8 and 12 months but there are reports of some specimens living as long as two years.
What’s really fascinating about the common jellyfish is that, when injured, it has the ability to heal itself. It uses a process known as symmetrization whereby, after amputation of a tentacle, the jellyfish rearranges its current body parts to allow full function to return.
2. Australian Box Jellyfish (Chironex fleckeri)
As the name suggests, the Australian box jellyfish is found in the coastal waters around Australia. However, there are more than 50 species of box jelly that can be found across Indo-Pacific waters, usually in shallower areas.
The Australian box jelly has certainly earned itself a reputation as being the most dangerous jellyfish in the world. Just one sting can kill a human in minutes, but even if you’re lucky enough to survive, there’s a risk of heart attack, inflammation, and other nasty symptoms. There are reports that around 40 people are stung and die by these creatures each year, but the number is likely a lot higher, with many people not reporting their bad luck.
Unlike other jellies, the box jellyfish has 24 eyes spread across its body giving it 360-degree vision. It feeds on small fish and shrimp and uses a propulsion technique by catching and expelling water to help it move as much as six meters a minute.
Also known as the sea wasp, these jellyfish have a boxy body and tentacles that are up to ten feet in length. They’ll live for around 12 months, but in captivity, it’s proven difficult to keep them alive for anywhere near as long.
3. Lion’s Mane Jellyfish (Cyanea capillata)
Want to meet the world’s largest species of jellyfish? It’s the lion’s mane jellyfish which can grow up to 6.5 feet (2 m) across its body with tentacles that can stretch as far as 121 feet (37 m)! For this reason, it’s sometimes called the giant jellyfish and is found in colder waters, particularly in the North Atlantic and North Pacific as well as the Arctic Ocean.
Lion’s mane jellies usually stay close to the surface and don’t usually swim any deeper than about 65 feet (19.8 m) where they can be found feeding on small fish and zooplankton. It catches prey using toxins from its sting and is armed with up to 150 tentacles, which it uses to bring the food to its mouth.
Humans don’t usually come into contact with the giant jellyfish, but if they do sting you then their neurotoxins may have a variety of effects. These can include skin rashes, breathing difficulties, headaches, and fainting.
4. Atolla Jellyfish (Atolla wyvillei)
The atolla jellyfish has a groove that runs along the body, making it look as though it is wearing a crown. This makes them easily identifiable, but you probably won’t come into contact with one as they live right down in the midnight zone, which is up to 13,100 feet (4000 m) and is shrouded in darkness. If you were unlucky enough to meet one, you’d better swim in the opposite direction, as a sting from one of these jellies could be fatal.
These jellyfish use their tentacles to catch prey, including a long, recoiling tentacle that’s thought to also be used in reproduction. They aren’t fussy about what they eat and will feed on anything that they can grab.
It may surprise you to learn that the atolla jellyfish doesn’t have any brain cells and yet is still able to arm itself against prey and survive in the depths of the world’s oceans. They aren’t huge jellyfish, usually not growing to more than eight inches (20 cm) in diameter with tentacles that extend up to 12 feet (3.7 m).
5. Irukandji Jellyfish (Carukia barnesi)
Many people live in fear of the name of the irukandji jellyfish and for good reason. This is one of the most venomous jellies in the world but that doesn’t mean they are totally fascinating. Found exclusively around the coastlines of Northern Australia, the irukandji jellyfish enjoys spending time around reefs in slightly deeper water.
While they may be one of the most dangerous, with a sting that can kill a human in minutes, these jellies are also one of the smallest. They don’t typically grow any larger than 0.98 inches (25mm) in diameter and have a tentacle that extends from each corner of the bell. The tentacles are not normally any bigger than a 3.3 feet (1 m) in length.
Irukandji jellies can sting with their tentacles as well as their bells and use this to kill prey such as small crustaceans and zooplankton.
6. Barrel Jellyfish (Rhizostoma pulmo)
The barrel jellyfish normally grows to around 15 inches (38 cm), but there are reports of those that have reached as large as 60 inches (152 cm) in diameter. These are some of the most interesting looking jellies, and are found in Atlantic and Mediterranean waters as well as in the Black Sea and as far down as South Africa.
These beautiful jellyfish can weigh as much as 25 lbs (11 kg), but despite their size, it is not much of a threat to humans since it is unable to pierce our skin to inject venom. For this reason, it’s easy to get up close and personal with them for divers and marine animal lovers.
They are normally found in coastal waters, particularly around the UK and Ireland, where they’ll normally be washed up on shore in the late spring and early summer. What sets them apart from other species are their eight frilly tentacles.
7. Atlantic Sea Nettle (Chrysaora quinquecirrha)
The sea nettle is so called because of its sting which is similar to that of a nettle, although some would compare it to a bee sting. In any case, the sting of the sea nettle is not dangerous to humans and will typically only cause localized pain for around 40 minutes. That said, there are some people that are allergic to the venom which can lead to more serious symptoms.
Sea nettles have a combination of thin and frilly tentacles which can grow up to 20 feet (6 m). Their bodies usually grow to around 3 feet (0.9 m), and they can live as long as 18 months, which is lengthy in comparison to some jellies.
The Atlantic sea nettle, as you may guess, is found in Atlantic waters, although there are other species of sea nettle that can be found globally. They prefer to stay near the surface of the water, where they will prey on anything from small fish and crustaceans to plankton and even other jellies.
8. Cannonball Jellyfish (Stomolophus meleagris)
The cannonball jellyfish can be found around the Pacific and Atlantic as well as gulf shores and has a rather unique appearance. With a ball-shaped body, this jellyfish does not have the long tentacles we see on other species but instead has 16 short oral arms.
They prefer warmer, tropical waters and are often found along the eastern coasts of North and South America. Here, they prey on a variety of sea animals, including fish eggs, and molluscs.
While a lot of jelly species rely on the movement of the water for transport, the cannonball uses its oral arms to move through the ocean.
The cannonball jellyfish does have a rather strange appearance, but it’s really nothing to be feared. They live for very short periods, up to six months and are often found washed up on shore where they won’t do much harm to humans. If you are stung, the worst that will happen is some minor skin irritation.
9. Nomura’s Jellyfish (Nemopilema nomurai)
With what looks like a mass of tangled plant roots, the Nomura’s jellyfish is one of the most poisonous animals in the sea. These giants can weigh as much as 440 lbs (200 kg) and are found around Japanese coasts, where they have instilled fear into local beachgoers.
While they are poisonous, the sting from the Nomura’s jellyfish is unlikely to be fatal, with only 8 deaths having been reported. That said, you’re in for a world of pain, as the sting can induce some pretty nasty sensations.
These jellies can live for up to two years but they reproduce so slowly that populations don’t get out of control. However, there are reports that this species is causing some problems for Japanese fisheries. To counter this, there are some Japanese vendors that are trying to flog Nomura’s jellyfish as a type of nouvelle cuisine!
10. Compass Jellyfish (Chrysaora hysoscella)
The compass jellyfish is truly one of the most beautiful looking jellies with brown markings that make the body resemble a compass. However, while these are stunning animals, they are also very dangerous, so we’re better off admiring them from a distance.
These jellies are usually found around North Atlantic waters as well as in Mediterranean areas. They’re a mid-sized jellyfish species that grows to around 12 inches (30.48 cm) and have 24 trailing tentacles. They are very common in UK waters where they are often found washed up on the shore in spring and summer.
Unlike other jellyfish species, the compass jelly is a solitary animal and will propel itself along the surface of the water in search of prey. However, most of their movement is reliant on the current. They’ll feed on a variety of invertebrates and plankton and are considered 100% carnivorous.
11. Mauve Stinger (Pelagia noctiluca)
While the mauve stinger only grows to around 4 inches (10 cm) across, its tentacles can grow to up to 10 feet (3 m)! These beautiful jellies come in a bluish purple color and a warty-looking umbrella. But even though they have a striking appearance, this is another species that should be admired from afar, as their sting really does pack a punch. When stung, the pain could last weeks along with symptoms like inflammation and vomiting.
The mauve stinger usually stays in the open ocean, so it’s unlikely you’ll see them on a trip to the beach. They live in northern waters and as far down as the Mediterranean. In the United Kingdom and Irish waters, they are very common. At night, they use bioluminescence to glow when they feel threatened!
This species of jellyfish likes to live in a smack with numbers in the thousands. In fact, it was once reported that there was a group of mauve stingers that covered more than 28 miles (45 km)! Within their groups, they will hunt small fish and crustaceans as well as plankton.
12. Amakusa Jellyfish (Sanderia Malayensis)
Amakusa jellyfish are another species that are native to Japanese waters. However, they only really make an appearance during the summer. Sometimes, these jellyfish can be found as far as Pakistan and Malaysia.
They grow up to around 8 inches (20 cm) with long tentacles and typically live for around 12 months.
The amakusa jellyfish is not so dangerous to humans that it can cause death but the sting has been known to cause immense pain and even tissue death.
13. White-Spotted Jellyfish (Phyllorhiza punctata)
You may hear the white spotted jellyfish being called the floating bell or the Australian spotted jellyfish. Some even called it the brown jellyfish, but whatever name it goes by, these are some of the least dangerous jellyfish to humans with a sting that does nothing more than cause mild irritation.
While the white spotted jellyfish is native to Australia and as far north as Japan, it has been introduced to other areas and so is now considered a global species. The main problem with this is that it is considered invasive and has caused problems for the populations of certain species of shrimp, on which it feeds.
These jellyfish are one of the best-looking species, with a spotted body and short arms that extend from the base of the umbrella.
14. Mushroom Cap Jellyfish (Rhopilema verrilli)
The mushroom cap jellyfish are commonly found along the Atlantic coasts of North America. Unlike a lot of jellyfish species, it does not have tentacles, although that does not mean that it cannot sting, it’s just that the sting is located within its bell.
This species of jelly takes its name because the bell is not dissimilar in appearance to the cap of a mushroom. It can grow as large as 20 inches (50.8 cm) in diameter and is often confused with the cannonball jelly. However, a good way to tell them apart is by their size with the cannonball being notably smaller.
Mushroom cap jellies feed exclusively on plankton and are one of the few species that not only inhabit coastlines but can also be found in estuaries.
The sting of the mushroom cap jellyfish is not fatal to humans although it will cause some mild pain and discomfort. Over in Japan, these jellies are eaten as a delicacy.
15. Jelly Blubber (Catostylus mosaicus)
The jelly blubber, sometimes called the blue blubber owing to its coloration, is a very common species along the coastlines of Eastern Australia. These jellies are often found swimming in large groups and prefer to stay in coastal waters as well as estuaries.
One of the distinguishing features of the jelly blubber is that it lacks a mouth. Instead, it has an opening at the end of its tentacles which is used to suck up plankton and small crustaceans. They often have milky coloration but as you go further north, the relationship with algae plant cells in its body means that the jellies take on more of a blue hue.
These unique-looking jellyfish don’t usually get any larger than around 14 inches (35.6 cm). While they can sting, this is not usually a problem for humans. The sting certainly won’t cause death, and the worst you’ll experience will be some mild redness and itching at the site of the sting.
16. Cauliflower Jellyfish (Cephea cephea)
The cauliflower jellyfish is sometimes called the crown jellyfish largely because of its unique appearance. These jellies have a bell-like shape with a warty appearance and can grow up to 23 inches (60 cm) in diameter. They have short tentacles which, as with other species, are primarily used to catch prey.
Cauliflower jellies are found in the waters around Northern Australia and right through the Indo-Pacific regions. In some East Asian countries like Japan and China, this jellyfish is eaten as a delicacy as well as being used for its medical properties.
As with other species, the cauliflower jelly can sting, but it will do nothing more than cause minor irritation for humans and certainly wouldn’t be fatal.
17. Upside-Down Jellyfish (Cassiopea spp.)
The upside-down jellyfish gets its name because the medusa tends to live on the bottom of bodies of water in an upside-down position. They are found in various locations, such as mangroves, swamps, canals, and mudflats in the warmer waters of the Caribbean and Florida, as well as in Australia.
Upside-down jellyfish are more likely to be found in groups and one of the most worrying things is that they can sting you without actually touching you. This is because the jellies will release a mucus that contains nematocysts (the things jellyfish use to sting) when they feel threatened. Just the very act of you moving through the water could cause this reaction.
While the severity of an upside down jellyfish can range anywhere from mild to severe, there are recorded deaths. You probably won’t notice them as they’ll be buried in the substrate but look out for small jellyfish up to around 5 inches (12.7 cm) that could be white, blue, green or brown in color.
18. Fried Egg Jellyfish (Cotylorhiza tuberculata)
Perhaps one of the most creatively named jellyfish on our list, the fried egg jelly really does resemble a sunny side up! They can grow up to 16 inches (40.6 cm) and have a flat yellowish-white bell with a central protrusion which is what makes it look so much like a fried egg. The jellyfish also has eight oral arms, which have black spotted markings.
The fried egg jellyfish can sting humans, but the effects are incredibly minimal. Even those who are sensitive to the toxins would only experience mild itching and redness at the sting location.
You will find the fried egg jellyfish in the Mediterranean sea where it feeds mainly on plankton. They are incredibly docile animals and while they are usually feared, there is really no need to be concerned about them.
How to Treat Jellyfish Stings?
There are a few species of jellyfish whose sting can be fatal to humans, and if you are unfortunate enough to be stung by one of these, you’ll need to seek urgent medical attention.
However, most jellyfish stings don’t cause too many problems for humans. The most common symptoms include skin rashes, inflammation, welts, and itching. The pain may be very local to the sting site or may radiate along the affected arm or leg.
If you are stung, you should not pee on the area, despite what urban myths may have you believe. Instead, take the following action:
- Rinse the sting site using seawater.
- Take a pair of tweezers or the edge of a credit card to remove any tentacles that are stuck to the skin.
- Use warm water to soak the affected area for at least 30 minutes.
- Use painkillers to manage your discomfort while the sting heals.
Effects of Global Warming on Jellyfish
We are all used to talking about the negative effects of global warming, but when it comes to jellyfish, it’s quite the opposite. Global warming is actually helping these creatures to thrive, and their numbers are growing.
One of the main reasons for their booming numbers is that global warming has decreased the oxygen in the ocean by around 2%. Jellyfish are easily able to thrive in areas with lower oxygen levels where other animals would struggle. For example, tuna, which is a common predator of the jellyfish, have decreased in numbers. This is also beneficial for the jellies since they’re not hunted as much.
However, because of these effects, it is estimated that we will soon start to see a serious imbalance between the number of jellyfish and other sea creatures.
