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The largest of the jellyfish is the so-called "lion's mane" (cyanea capillata): its magnificent bell can reach up to 2.5 meters in diameter with 30-meter tentacles.

Not only beautiful, though. Its tentacles are in fact an incredible defense tool and release toxic substances that can even lead a man to death. Famous solution of one of the cases of Sherlock Holmes (The adventures of the Lion's Mane): "The murderer? A cyanea!"

In Focus 120 (October 2002) an extraordinary reportage on these "underwater spaceships" (pp. 234-240).

The Aurelia aurita is a jellyfish widely distributed throughout the Mediterranean, also called four-leaf clover since it has four horseshoe-shaped gonads placed on the walls of the gastrovascular cavity. Looking at the jellyfish in transparency, she looks tattooed with a large yellowish-white four-leaf clover.

The stinging cells of the jellyfish are instead present on the entire surface of the umbrella (which can reach 45 centimeters in diameter), on the tentacles and on the handlebars.

© NOAA

Is there better protection than can be found among the long tentacles of a jellyfish? Some fish (usually very young) seem to think so, seeking shelter from possible predators right there, "in the arms" of a Thysanostoma loriferum, a jellyfish that lives in the Pacific Ocean, around the Hawaiian islands (USA). It is a sort of symbiotic association called commensalism, which is created in the animal world when one of the organisms takes advantage of the relationship with the other that, for its part, receives neither damage nor utility. In this specific case, the fish enjoy the company of the jellyfish, which is not disturbed.

The shape of the jellyfish body (in the photo, one of the genus Cephea) can be compared to that of a mushroom with an umbrella of various shapes: a ring, as in this case, a disc, piriform (pear shape) or even cubical. It is this muscular structure that contracts by allowing the jellyfish to move in the water. The tentacles rich in stinging cells called cnidoblasts, through which the preys are stunned and killed, but also irritated are the men who come into contact with it. The gelatinous body is due to the fact that, between the outer and inner cellular layer, there is a patina very rich in water, called mesoglea. Cephea jellyfish are found mainly in the warm tropical waters, such as those of the Red Sea, where the photo was taken.

Here are the extraordinary images found in front of the visitor of the exhibition that took place at the Ocean Park in Hong Kong entitled "Spectacular sea jellyfish". In 280 square meters, extraordinarily illuminated and animated with special effects, a thousand jellyfish floated.

Putting these animals in an aquarium is a rather complicated affair that requires a lot of precautions: just a bump and a sizzle with a rough wall to break or hurt these fragile creatures and 90 percent composed of water. To learn more, read here .

Think of finding you, while swimming in the sea, in front of the largest jellyfish in the world …

But this is not just any sub, he is a researcher who is attaching a sensor to Echizen's jellyfish, a Japanese coastal area. The large jellyfish can reach a meter and a half in diameter and can weigh 150 kilos. Local fishermen said they had seen herds of thousands of specimens.

And while the fishermen are damaged in part by the great jellyfish, which is found in the waters of the Sea of ​​Japan, especially in autumn, researchers will use this large specimen, thanks to some sensors connected to a satellite, to take information on the sea's temperature in depth .

They manage to avoid any obstacles even at the last moment and change direction in no time. Almost as if they had a hundred eyes!

In reality, however, it is not the amount of eyes that make these animals very clever, but the ability to use them appropriately. Species living for example in the Caribbean Sea have developed an upward view (on the surface they often meet branches of trees). While the jellyfish that live in the depths have "low" eyes able to avoid obstacles by capturing the slightest variation in light intensity. A capacity for processing the latter which, according to experts, is very particular for an animal that does not have a brain and has an elementary nervous system.

© Anders Garm

These jellyfish have a poetic name, they are called four-leaf clover (Aurelia aurita), but they are fearsome "predators" for the marine world. They feed on micro-organisms such as molluscs, crustaceans, protozoa and diatoms by catching them with tentacles. Certain delicacies are in fact, trapped on the mucosal surface of the tentacles and then with a contraction, are carried directly to the "mouth", in reality it is a gastrovascular cavity where food is absorbed and digested. From the analyzes of some enzymes the researchers have noticed that these jellyfish need a very varied diet, rich in carbohydrates and proteins.

At a glance, in the dark blue depths of the northernmost seas, it is striking for its bright orange color. But it is the tangle of tentacles that give the name to this jellyfish, of the Cyanea capillata species. The confused and tangled mass of arms, which seems to increase along with the age of the "owner", earned her the name of lion's mane jellyfish. The bell, or umbrella, of this creature "in jelly" oscillates between 30 and 80 centimeters in diameter, but some individuals reach the record dimensions of 180 centimeters. The contact with one of these specimens can be dangerous for humans - the tentacles are strongly stinging - but fortunately, to the warm Mediterranean waters the swimmer prefers the colder regions of the oceans, the Baltic Sea and the North Sea.

The first interactive map of jellyfish in the Italian seas

You might also like: Jellyfish are coming !! A lake of jellyfishes Giant from the depths Do you want an ice cream that you see in the dark? It is based on jellyfish A mane of tentacles The largest of the jellyfish is the so-called "lion's mane" (cyanea capillata): its magnificent bell can reach even 2 and a half meters in diameter with 30-meter tentacles.
Not only beautiful, though. Its tentacles are in fact an incredible defense tool and release toxic substances that can even lead a man to death. Famous solution of one of the cases of Sherlock Holmes (The adventures of the Lion's Mane): "The murderer? A cyanea!"
In Focus 120 (October 2002) an extraordinary reportage on these "underwater spaceships" (pp. 234-240).