Medusa, the future master of the seas?

Medusa, the future master of the seas?

Jellyfish and mythology

Linnaean jellyfish

It is the famous Swedish botanist Carl von Linné, who in the XVIIIth century described these bell-shaped creatures with snake-like tentacles.

He named them “Medusas” in reference to one of the three Gorgons (Stheno, Euryale and Medusa) of Greek mythology. These snake-haired monsters turned anyone who looked at them into stone. Medusa was reputed to be deadly.

As a botanist, Linnaeus described jellyfish with pistils and stamens.

Cuvier also saw the jellyfish as close to the plant world, with a root-shaped mouth. It was the naturalist François Péron, who in the 19th century, described the jellyfish as the animal it really is.

He kept two elements from the mythology dear to Linné: the seasonality of jellyfish was due to their regular migration to the Abyss, like the Gorgons. And when he established the very first classification of jellyfish, he gave them the names of characters gravitating around the Gorgons (Cassiopeia, Chrysaor, Geronus). In this way, scientists familiar with mythology would identify them more easily.

Description of this animal

The jellyfish is a marine invertebrate animal in the shape of a bell or “umbrella” surrounded by fine retractable tentacles (up to ten times the diameter of the umbrella) and in multiples of four: up to eight hundred tentacles depending on the jellyfish!

From the center of the umbrella, hangs freely the “manubrium”, organ that connects the mouth to the stomach located at the top of the umbrella.

The radial channels

From the stomach, the “radial canals” carry the products of digestion to the circular canal that surrounds the parasol. The products of excretion take the opposite route to be regurgitated by the mouth.


From the Greek “knidé” which means nettle, jellyfish are one of the two groups of cnidarians: marine animals consisting of a mouth surrounded by tentacles.

They exist in two forms corresponding to the two stages of their life: in the form of static polyps, because they are attached to a support, which give rise to mobile jellyfish, which live according to the currents.

Plastic is an excellent support for jellyfish polyps: plastic pollution in the sea, in particular plastic micro-particles, are an important cause of jellyfish blooms.

Jellyfish and sea water density

The soft body of the jellyfish is composed of a gelatinous substance, the mesoglea, which is 98% water. A composition that varies according to the salinity of the sea water: thus the jellyfish Aurelia aurité is composed of a little more than 95% of water in the Mediterranean, but 97.9% in the North Sea and 98.2% in the Baltic.

The similar density between jellyfish and sea water allows them to float according to the currents.

Since the dawn of time
The jellyfish has existed for more than 600 million years. At the embryonic stage, it is formed of two layers: an ectoderm (which produces the epidermis and the nervous system) and an endoderm (which produces the digestive tract), the gelatin layer between these two layers gives it its body consistency.

But in the evolutionary scale, these simple animals, with two layers (or “diploblastic”), are nevertheless the very first multi-cellular animals.

An evolved species

Scientists believe that the separate circulatory systems (digestion and excretion) of the jellyfish are a foreshadowing of the circulation of vital fluids (the bloodstream) in evolved species. Similarly, the sensory system of the jellyfish is thought to be the very first brain embryo in Creation.

What attracts jellyfish?

Researchers at the University of Lund in Sweden have uncovered the way tropical jellyfish, the cubomedus, orient themselves. They have multiple eyes, which all look upwards: this vision is due to gypsum crystal in the structures surrounding their eyes.

These jellyfish are said to orient themselves according to the surface, detecting what is happening up to eight meters away. An astonishing “vision”, considering their primitive nervous system.

Why can a jellyfish be dangerous, even deadly?
The jellyfish is a venomous animal: its tentacles are equipped with stinging filaments or “cnidocysts” which inject venom that serves to paralyze its prey.

For humans, most jellyfish are harmless: but the sting of some species ranges from painful burns to fatal stings.

Jellyfish in the Mediterranean

In the Mediterranean, it is the Pelagia noctiluca, which spoils swimming: the pain comes from the fact that the cnidocysts remain stuck on the skin and continue to inject venom into the wound.

In Australia, the chironex is the most venomous animal in the ocean. Each of its tentacles contains billions of stinging cells. The cubomedusa is capable of killing a human being by cardiac paralysis.

Thus, every year, about fifty people die from a tropical jellyfish sting: while less than ten die from a shark attack!

How to relieve the pain ?

In case of a jellyfish sting, forget two preconceived ideas: urinating on it and rinsing it with fresh water will only make the pain worse.

The venom does not tolerate heat above 45 degrees: the way to relieve the pain is to rinse the burn with sea water (with baking soda if you have some on hand) and to heat it (with hot sand on the beach, a hair dryer at home).