Sea jellyfish facts


Jellyfish are considered one of the most ancient creatures that have ever lived on the planet. They lived on Earth long before the advent of dinosaurs. Some species are completely harmless, while others can kill with one touch.

According to research, the life of the first jellyfish originated on the planet more than 650 million years ago. Before some marine life began to migrate to land. From the Greek language, Medusa is translated as the patron saint, the sovereign. The animals, commonly referred to as jellyfish, belong to the Cnidaria family of over 10,000 species. However, some jellyfish-like animals, such as comb jelly, belong to the Ctenophora family. Jellyfish are invertebrate marine animals with a transparent gelatinous body, along the edges, equipped with tentacles. They are the lowest multicellular creatures, belongs to the type of coelenterates. Animals of this type have the appearance of an open bag at one end. The hole serves as a mouth, which is surrounded by a corolla of tentacles. The mouth leads into a blind-closed digestive cavity (gastric cavity). Digestion of food occurs both inside this cavity and by individual cells of the endoderm – intracellularly. Undigested food debris is excreted through the mouth. Since the creatures are 95% water, 3% salt and 1-2% protein, their body is almost transparent, with a slight tint.

red jellyfish

Tentacles are located along the edges of the body, the appearance of which directly depends on which species it belongs to: in some they are short and thick, in others they are long and thin. Their number can range from four to several hundred (but at the same time it is always a multiple of four, since the representatives of this class of animals are characterized by radial symmetry).

These tentacles are composed of string cells, which contain poison, and therefore are directly intended for hunting. Interestingly, even after death, jellyfish are able to sting for another half a month. Some species can be deadly, even to humans. For example, the animal known as the “Sea Wasp” is considered the most dangerous poisonous animal in the world’s oceans: scientists say that its poison is enough to poison sixty people in a few minutes.

These animals grow throughout their life, and their size largely depends on the species: among them there are very small ones, no more than a few millimeters (1/16 in), and there are also huge ones, the body size of which exceeds 6.5 feet (2 m), and together with the tentacles – and all 100 feet (30 m) (for example, the largest jellyfish in the world ocean, Cyanea, which lives in the Northwest Atlantic).


Despite the fact that jellyfish do not have brains and sense organs, they have light-sensitive cells that act as eyes, thanks to which these organisms are able to distinguish darkness from light (they, however, cannot see objects). Interestingly, some specimens glow in the dark: those living at great depths glow red, and those closer to the surface glow blue. This light helps to attract prey or scare away predators.

Jellyfish habitat

Jellyfish live in salt water, so you can stumble upon them in almost any sea or ocean (with the exception of inland seas). Sometimes they can be found in closed lagoons or salt lakes on coral islands. Some representatives of this type are thermophilic and live on the surface of water bodies well warmed by the sun, like to splash on the shore, while others prefer cold waters and live only at depth. The area is very wide – from the Arctic to the tropical seas. Only one species of jellyfish lives in fresh water – Craspedacusta sowerbii, which swims in the waters of South America.

What do jellyfish eat?

The diet of jellyfish consists mainly of plankton: small crustaceans, small fish, fish eggs, zooplankton, eggs of marine life, smaller relatives. Jellyfish catch prey with dexterous tentacles. Some species have cells on their tentacles that secrete paralytic venom. Many jellyfish are passive hunters. They wait for the victim to swim up to shoot him with their poisonous tentacle.

Jellyfish habitat


Another interesting feature of jellyfish is their ability to restore lost body parts – absolutely all cells of these animals are interchangeable: even if this animal is divided into parts, it will restore them, thus forming two new individuals! If this is done with an adult jellyfish, an adult copy will appear, from a jellyfish larva – a larva.

Some jellyfish are immortal

There are two phases in the life of jellyfish: the stationary polyp stage and the mobile jellyfish stage. This is the medusa-phase. Usually jellyfish start out as polyps and turn into jellyfish, but the Turritopsis jellyfish has been nicknamed the “immortal jellyfish” for its ability to return to the polyp stage during stress.

jellyfish live

Reproduction of jellyfish

Creations reproduce sexually or vegetatively. In the first variant, sperm and eggs mature in the gonads, after which they leave through the mouth and are fertilized, during which a planula, a larva, is born. Soon, the larva settles to the bottom and attaches to the stone, after which a polyp is formed, which, in turn, multiplies due to budding. On a polyp, daughter organisms overlap. When a full-fledged jellyfish is formed, it flakes off and floats away. In other species, polyps form in the gonads and, bypassing the intermediate stages, babies appear from them. The newborn jellyfish feeds and grows, turning into an adult with mature genitals and a willingness to reproduce. After breeding, jellyfish most often die – they are eaten by natural enemies or thrown ashore.

Natural enemies

Despite their poisonous defenses, jellyfish cannot do without enemies. Tuna, shark, swordfish, marlins, sea turtles and even some species of salmon are all natural enemies.