Jellyfish are one of the most feared animals that inhabit the oceans, generally because of their painful and even deadly sting on certain occasions. There are also legends of giant jellyfish capable of sinking ships. There is no denying that many jellyfish are dangerous, but it is their way of feeding. They do not actively hunt their prey, simply waiting patiently for it to fall onto their long tentacles.
In this article on our site we talk about 22 types of jellyfish that exist, each one more surprising than the last. Immortal, poisonous, giant… You'll love discovering them!
Characteristics of jellyfish
Jellyfish make up a phylum of animals called Cnidaria. It includes some 10,000 species of jellyfish of which only 20 species are freshwater, the rest are marine. Its body is characterized by having radial symmetry, that is, we can divide the animal with imaginary lines and get many equal parts.
For example, all vertebrate animals have bilateral symmetry, we can only divide ourselves into two equal parts, right and left. It is also one of the animals without a central nervous system. Some of the characteristics of jellyfish that we can highlight are:
- The body of jellyfish is organized as a blind sac with a single hole: it acts as an entrance for food and an exit for waste that it is located in the lower or apolar area, that is, it acts as both mouth and anus at the same time.
- Inside this sac we find a digestive cavity called gastrovascular cavity, gastrocele or coelenteron: it acts both by digesting food and sending nutrients and oxygen to the rest of the body.
- They have an umbrella: it is the pole opposite the mouth that is shaped like a bell or umbrella, constituting the characteristic umbrella of These animals.
- Despite their simplicity, jellyfish have highly developed sense organs: located on the edge of the umbrella. Here we find visual organs, called ocelli and stationary organs known asstatocysts , used to maintain balance
- These animals also have some specialized cells known as cnidocysts: Among the jellyfish, we find several types of cnidocyst, the most common, the nematocyst This type of cnidocyst is stinging, whose function is hunting and defense. The nematocyst is found in the tentacles of these animals and, through them, they cause bites. Another important type are the pticocysts , these secrete a mucus that serves to capture small animals or nutritious particles.
Another very important characteristic of this group of animals is that they have two body forms:
- The polyp form: which is generally benthic and lives anchored to the seabed, it is also frequently colonial.
- The jellyfish form: planktonic and usually solitary.
There are species that only have the polyp form, others only jellyfish and others that have both forms in their life cycle.
Where do jellyfish live?
Jellyfish are aquatic animals, so outside of this environment they dry quickly since 90% of their body is water, hence they are commonly known as "aguamala" or "aguaviva". These animals are planktonic, that is, they live free in the ocean without being anchored anywhere. They are carried by currents of cold and warm waters through the oceans, they can only actively move up or down in the water column.
Check out this article on our site about Where Do Jellyfish Live? for more information on the subject.
What do jellyfish eat?
Jellyfish can be predatory or suspensivorous, so they either actively hunt fish or filter the water around them, thereby trapping small food particles. To hunt fish, in its tentacles we find cnidocysts, cells that have an internal capsule filled with stinging or sticky liquid, depending on the type, and a filament. It is fired by a cilia called cnidocilium sensitive to touch.
Prey pursuit is not active. The fish must get too close to the jellyfish and brush its tentacles, which can sometimes be several meters long and imperceptible, to activate the cnidocysts. When the fish stops moving, with the help of the tentacles they bring it closer to the mouth, passing into the digestive cavity.
For more details on the subject, do not hesitate to consult the following article on What do jellyfish eat?
Poisonous Jellyfish
Now that we have seen their characteristics, as well as where they live and what they eat, let's learn about some examples of poisonous jellyfish. Not all jellyfish are poisonous, it all depends on the type of cnidocyst they have.
Only those that have nematocysts are considered poisonous and cause the death of their prey through a stinging liquid that affects the system highly strung. Some poisonous species of jellyfish are:
- Sea nettle jellyfish (Chrysaora fuscescens).
- Lion's mane jellyfish (Cyanea capillata): it is also a type of giant jellyfish.
- Portuguese man-of-war or Portuguese jellyfish (Physalia physalis).
- irukandji jellyfish (Carukia barnesi).
- Sea wasp (Chironex fleckeri).
- Cannonball jellyfish (Stomolophus meleagris).
- Common jellyfish (Aurelia aurita).
- Blue jellyfish (Rhizostoma pulmo).
- Luminescent jellyfish (Pelagia noctiluca).
- Radiated acalefo or aguamar (Chrysaora hysoscella).
Are there jellyfish that don't sting? Discover the answer.
Giant jellyfish
Jellyfish classes have a wide range of sizes. Some are so small that they could fit on a fingertip, as is the case with the irukandji jellyfish. However, its sting is no longer highly dangerous.
Other jellyfish have gigantic sizes, exceeding two meters in diameter and weighing more than 200 kilograms. If we also measure the tentacles, some jellyfish can measure more than 30 meters in length, for example the arctic lion's mane jellyfish, which is also a of the largest jellyfish. But none can compete with the giant jellyfish nomura (Nemopilema nomurai) with more than three meters in diameter
Immortal jellyfish
Some jellyfish have a special ability that makes them immortal We are talking about the Turritopsis nutricula species. This species of jellyfish, once it reaches its adult state, that is, the phase of its life in which it reproduces and, in addition, has the shape of a jellyfish, it is capable of returning to its polyp state, attaching itself to the seabed again until the environmental conditions are conducive to return to its adult state.
If you want to know more about the reproductive cycle of the types of jellyfish, don't miss our article on The reproduction of jellyfish.
Types of jellyfish in the Mediterranean
In the Mediterranean Sea we can find several species of jellyfish, some of them dangerous and their presence on the shores leads to a ban on swim on the beaches. The names of Mediterranean jellyfish are:
- Portuguese man-of-war (Physalia physalis).
- Radiated acalefo or aguamar (Chrysaora hysoscella).
- Fried egg jellyfish (Cotylorhiza tuberculata).
- Luminescent jellyfish (Pelagia noctiluca).
- Moon jellyfish (Aurelia aurita).
- Aequorea jellyfish (Aequorea forskalea).
- Jellyfish aguamala or aguaviva (Rhizostoma pulmo).
- Cubo jellyfish (Carybdea marsupialis).
- Inverted jellyfish (Cassiopea andromeda).
- Sailboat jellyfish (Velella velella).
Also discover on our site the Most dangerous animals in the Mediterranean.
