Jellyfish Curiosities

Jellyfish Curiosities

Jellyfish are mysterious creatures of the ocean with their sinuous, translucent, and unexpectedly coloured bodies. Its way of living and reproducing has unique processes that never cease to amaze the scientific community and that could revolutionize the medicine of the future.


In this article, we discover fun facts about jellyfish and reveal some of their most striking features. Dive into the fascinating world of this animal.

They’ve been around for millions of years

Jellyfish have existed on Earth for millions of years; more specifically, 600 million years , according to the Ministry for Ecological Transition and Demographic Challenge of the Government of Spain. The earliest fossils attributable to jellyfish date back to neither more nor less than the Primary Age. Today, the common jellyfish or moon jellyfish continues to arouse much curiosity among marine biologists.

They mainly consist of water.

Jellyfish are animals belonging to the Cnidarian family. As we know, their morphology is bell-shaped, thanks to which they are able to move in water with their characteristic rhythmic contractions. Thanks to their anatomy, made up of 95% water, Jellyfish have a series of attributes (luminescence, ability to cause urticaria, etc.) that make them curious and fascinating beings.

The mouth also works as an anus.

Jellyfish are carnivorous animals and, as such, have a digestive system that allows them to assimilate and metabolize their prey. Jellyfish, although it may not look like it, do have a mouth, but in a somewhat unexpected place: their mouth is located at the bottom of their anatomy and serves both for ingesting food and for excreting faeces. The mouth also leads directly to what is known as the “gastrovascular cavity”, ie the space where digestion takes place. This is one of the lesser-known curiosities of jellyfish.


The bioluminescence, or the ability of some living organisms to produce light, is another curious fact about jellyfish that you may have seen in aquariums or on the beach at night. These animals transform chemical energy into light energy to fend off predators, attract prey, or court potential mates. [1] .

In the case of jellyfish, this reaction can occur in symbiosis with a certain type of bacteria or extracellularly.

They don’t have brains or blood

Another curious thing about jellyfish that never hurts to know is that these animals don’t have brains as such. Her body could be described, pure and simple, as a sort of moving bag of water. As we mentioned before, jellyfish are 95% water and their bodies are made from a number of tissues very different from humans.

According to Dr Lucas Brotz, from British Columbia University and a well-known researcher of the Cnidarian family, the anatomy of the jellyfish is composed of two layers of thin cellular tissue, between which an inert and aqueous material is located. His research points out that the size of jellyfish, as well as the variation that its population experiences, is directly related to the impact of human beings on the coast and in the marine environment. [2] . This fact is not insignificant: for 600 million years, jellyfish have survived several mass extinctions. Discovering the secret of its adaptability will allow us to anticipate future environmental catastrophes.

They bite even after your death

Have you ever stepped on the body of a jellyfish that was thrown on the beach? It’s not easy to distinguish them: their transparent and sticky bodies end up buried by the sand, which makes them a risk for vacationers who walk along the shore. If you’ve ever stepped on one by accident, you know that the tentacles of a dead jellyfish still produce hives, albeit to a lesser degree.

The pungent cells in which jellyfish in particular and cnidarians, in general, are called cnidocysts. When they come into contact with possible prey, they use a series of filaments equipped with thorns to inoculate the venom. Changes in temperature often reactivate these cells, so if you are stung by a jellyfish, rinse the wound with room temperature saltwater.

They have different types of reproduction.

Another curiosity of jellyfish is that they do not have a single form of reproduction. These animals are characterized by having what is known as generational alternation, which consists of presenting, on the one hand, asexual reproduction through sessile polyps and, on the other, sexual reproduction through free-living jellyfish.

Jellyfish are oviparous and lay hundreds of eggs, which hatch between the mother’s tentacles. When they hatch, the larvae known as papules hatch, looking for a suitable place to attach and become a polyp. From here, depending on the type of jellyfish, the development of these animals will vary enormously. Find out how jellyfish are born in this other article.

Among them is one of the most feared animals.

The sea wasp ( Chironex fleckeri ) is considered the most venomous jellyfish of all, and one of the most dangerous animals in the world [3] . It lives in Australia and its venom is created to quickly paralyze its prey, causing serious damage that ends up being fatal, even to humans. This is because its venom includes hundreds of toxins.

There is a kind of giant size

The giant lion’s mane jellyfish ( Cyanea capillata ) is recognized worldwide for being the largest jellyfish in the world, which is one of the curious facts about the most surprising jellyfish. The body of this species can reach almost 4 meters in diameter and its tentacles almost 40 meters in length . Anyway, we are facing an imposing and, without a doubt, incredible animal.

The smallest jellyfish is one of the most poisonous

Known as the jellyfish Irukandji ( Carukia Barnes ) has a body that measures about 35 mm in diameter and tentacles only 1.2 cm in length [4] . Therefore, it is considered the smallest jellyfish in the world. However, despite its small size, it is known to be the second most poisonous jellyfish in the world, even though it becomes fatal if treatment is not received in time.

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