Jellyfish are ubiquitous in the seas and oceans. Some of them are beautiful, some look frightening, and among them there are both completely harmless creatures and deadly ones.
Fact number one.
Jellyfish have no brain. Having no brains, jellyfish are simple creatures. They consist of three layers: an outer layer called the epidermis; a middle layer of a thick, elastic, jelly-like substance called the mesoglue; and an inner layer called the gastrodermis.An elementary nervous system, or nervous network, allows jellyfish to sniff, detect light, and respond to other stimuli. The jellyfish’s simple digestive cavity acts as a stomach and intestine with one opening for the mouth and anus.
Fact number two.
95% or more (up to 98%) of the mesogloe layer of jellyfish consists of water, but it also contains collagen and other fibrous proteins, as well as stray amebocytes which can absorb debris and bacteria.
Fact number three.
Jellyfish can sting you, even if they are dead. Perhaps your parents warned you as a child at sea not to touch jellyfish on the beach because they can sting you. And this is indeed true. Jellyfish tentacles have tiny stings called nematocysts, which can detach, stick to your skin, and secrete venom.The amazing thing is that even if the jellyfish is dead, it can still bite you, because the cell structure of the nematocysts persists long after the animal is dead. Nematocysts release a filament containing venom when a foreign object touches the cell, and will continue to release venom until the cells are removed.
Fact number four.
Some jellyfish have teeth. Rattlesnakes (Beroid comb jellyfish / Ctenophora) have hundreds of small rows of cilia in their mouths that act like teeth and help them chew their prey.
Fact number five.
Some species of jellyfish are immortal. Turritopsis nutricula, better known as the «immortal jellyfish,» can change and transform its cells to go from an adult to a younger creature and vice versa. By the way, such metamorphosis can be repeated countless times. It turns out that this species of jellyfish may be biologically immortal, except that they can be eaten by predators. Usually, adult jellyfish produce larvae, which settle underwater.
The larvae then develop into polyps. The polyps then bud new jellies, which grow into adults, and the cycle begins again. Turritopsis nutricula can reverse this process — returning to the immature polyp stage after it grows into a mature individual.
Fact number six.
Cubomedus have tentacles that reach up to 3 meters in length. During the hunt, the tentacles of these jellyfish thin out and extend up to 3 meters in length. Up to 15 tentacles, which can be up to 3 meters long, grow from each corner of the cubomeduse’s body, which resembles a bell-shaped bowl. Each tentacle has about 5,000 stinging cells, which are not activated by touch, but by the presence of a chemical substance on the outer layer of the victim.
Fact number seven.
Some jellyfish can glow in the dark. Many jellyfish have bioluminescent organs that emit light. This light can help them in various ways, such as attracting prey or distracting predators.
Fact number eight.
Jellyfish can clone themselves. If a jellyfish is cut into two pieces, the pieces of the jellyfish can regenerate and create two new organisms. Similarly, if a jellyfish is damaged, it can clone itself and potentially produce offspring.
Fact number nine.
The first jellyfish, which appeared on Earth long before the dinosaurs, have hardly changed in 650 million years of evolution. They still evolved from polyps like beetles from larvae or butterflies from caterpillars. In total, scientists have studied and described about 3,200 species, and some of them are deadly — they can kill an adult with a single touch.
Fact number ten.
On land, all jellyfish turn into shapeless lumps of slime, because they are unable to maintain their shape outside the aquatic environment. At the same time, they are surprisingly strong — some of them live at great depths, and feel perfectly well there, despite the monstrous pressure. It is deep-sea jellyfish that are the largest invertebrates living at extreme depths.
On November 3, the world celebrates World Jellyfish Day every year. This unusual holiday is dedicated to invertebrates that have existed on earth many years longer than humans.
There is no exact date of World Jellyfish Day creation, but the initiators of the holiday are most likely a group of marine biologists, who were fascinated by these strange and at the same time beautiful creatures.
