Jellyfish are 98% water: true or false?


These marine animals are intriguing both for their majestic beauty and their organic complexity. Jellyfish are true mysteries for science and continue to surprise specialists. A rumor is circulating stating that jellyfish are made up mainly of water. Let’s lift the veil on the subject.

Jellyfish: fascinating animals with a thousand facets

The jellyfish comes in several sizes ranging from a few centimeters to 2.5 meters in diameter. They are both transparent and colored and their shape is also variable. For example, the Cyanea capillata species, better known as the “lion’s mane jellyfish”, is one of the largest and has up to 800 tentacles!

The umbrella constitutes the main organ of their body, then more or less numerous filamentous tentacles escape from it. Being flaccid and translucent, it is often difficult to see them in the water, as they become one with their surroundings. This is why they manage to bite us without us even noticing their presence. Moreover, their venom is among the most dangerous in the world.

Jellyfish also have the particularity of not having a heart or a brain! However, they are alive and well and have even survived all phases of mass extinctions, reigning over the oceans for more than 600 million years.

A little dry matter and a lot of water

The jellyfish is made up of 2% dry matter and… 98% water! Indeed, the only palpable membrane of which it is made is the umbrella and its few filaments. This has the shape of a “double-walled bag” containing a jelly called mesoglea. From the center of this umbrella hangs the manubrium which is a long organ on which the animal’s mouth is implanted at its end. This can be surrounded by arms or lips depending on the species. When it feeds, the food rises into the manubrium and lands in the stomach at the level of the umbrella.

Being one with the ocean or sea in which it lives, it cannot resist the sea currents that carry it. However, she is also capable of moving under her own power, by contracting her umbrella to make a sort of “leap”. The jellyfish breathes through its body wall.

Among the hundreds of varieties of existing jellyfish, all are constituted this way because these invertebrate animals have no shell, carapace or vertebrae. The water they contain contributes to their perfect flotation. Some species have eyes as advanced as ours since they are composed of a cornea, a lens and even a retina.

Jellyfish inhabit all the salty waters of the world

With the exception of one species of jellyfish which has adapted to fresh water, all of them live in the oceans and seas, whether on the surface, but also in the seabed. Some jellyfish prefer the shores, others the depths. They are even found in the abyss where darkness reigns. However, they, which appreciate warm currents, have adapted to very cold temperatures as well as heavy pressure and lack of oxygen.

With global warming and the scarcity of large predatory fish, we are witnessing an exponential growth of jellyfish in the waters and particularly around beaches. Although they seem harmless at first glance, their venom is formidable and causes (at best) very severe pain for around 30 minutes minimum.

Man, however, knows how to take advantage of this proliferation. In fact, no less than 25 species of jellyfish are edible and end up on our tables as chips, salads or even noodles. In biology, the fluorescent protein GFP from Aequorea Victoria has become essential for many experiments. In addition, they are used in the composition of certain medications, but are also used in space research. They are also excellent fertilizers when dried and their venom is no longer a threat.

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