Predation

Jellyfish are carnivorous and feed on plankton, small crustaceans, polychaetes and even small fish. Due to the mechanical and chemical stimulation of food, hydrozoans extend their tentacles and release nematocysts to wrap, paralyze, and poison the prey, and then bring the food into their mouths. The mucus secreted by the glandular cells in the oral area is beneficial to the swallowing of food. After the food enters the gastric cavity, the glandular cells in the gastric layer begin to secrete proteases to decompose and digest the food to form many polypeptides. At the same time, due to the flagellar movement of the nutritional muscle cells in the gastric cavity, the food be mixed and promoted. After this extracellular digestion, the intracellular digestion process begins. The pseudopodia that nourish muscle cells engulf food particles and form a large number of food bubbles within the cells. After acidic and alkaline chemical processes, nutrients diffuse from the cells. Effects are delivered throughout the body. The structure of the stomach cavity of bowl jellyfish and corals is relatively complex.

There are various radial tubes and circular tubes in the stomach cavity of the jellyfish, and there are gastric filaments of endodermal origin in the gastric pouch; the gastric filaments contain a large number of stinging cells and glandular cells, which are responsible for swallowing food. The stomach cavity is followed by killing and digestion. Digested nutrients are transported throughout the body through various channels, while undigested food residues are still excreted through the mouth. Glycogen and fat are the main storage materials of coelenterates.

***生

Although jellyfish look beautiful and docile, they are actually very ferocious. Because jellyfish have no respiratory organs and circulatory systems, only primitive digestive organs, the captured food is immediately digested and absorbed in the coelenter. Once a jellyfish encounters its prey, it never lets it go easily. But just like a rhinoceros living with a bird that cleans it of parasites, a jellyfish has its own reproductive partner. It was a kind of double-fin pomfret (Nomeus gronovii), commonly known as the little herd fish. It was only 7 centimeters long and could swim freely among the tentacles of the jellyfish without being afraid at all. When encountering a big fish approaching, the small herd fish swims to the middle of the tentacles under the giant umbrella, using it as a safe "refuge". It uses the device of jellyfish stinging cells to cleverly avoid the enemy's attack. Sometimes, small herd fish can even lure big fish into the hunting range of jellyfish and kill them, so that they can also eat the leftover bits and pieces of jellyfish. So why don’t the stinging cells on the jellyfish’s tentacles harm the small herd fish? This is because the small herd fish moves nimbly and can cleverly avoid poisonous threads, making them less vulnerable to harm. However, occasionally they die accidentally from poisonous threads. The jellyfish and the small herd fish live together and use each other. The jellyfish "protects" the small herd fish, and the small herd fish swallows the small creatures that live on the jellyfish.

The shape of the jellyfish is completely like condensation, its color is reddish purple, and it has no mouth or eyes. There is an object under its belly, and shrimps cling to it and swallow the saliva. Most of their lifespans are only a few weeks or months, and some live for about a year. Some deep-sea jellyfish can live longer.

Movement

Jellyfish shrink the shell and squeeze the inner cavity, change the volume of the inner cavity, spray out the water in the cavity, and move through water jet propulsion. Muscle fibers in the jellyfish epidermis extending from the tip to the end of the umbrella control the contraction and expansion of the lumen. The inner cavity expands, and the water is slowly sucked in, filling the inner cavity; the inner cavity contracts rapidly, squeezing the water out of the cavity, and the thrust generated by the water spray makes the jellyfish move along the axial direction of the body.

When a jellyfish attempts to sink in the water, its tentacles extend upward in a long line shape; when it attempts to rise or move in a certain direction, the distal end of the tentacles bends against the direction of movement. Jellyfish use their tentacles to effectively change the direction of movement. Jellyfish are not good at swimming and often rely on wind, waves and currents to move. Morphological characteristics depend on simple movement patterns. Some jellyfish have special glands in their bell-shaped bodies that emit carbon monoxide, causing the bell-shaped bodies to swell. When the jellyfish encounters enemies or encounters a big storm, it will automatically release its gas and sink to the bottom of the sea. When the sea is calm, it only takes a few minutes for it to produce gas to expand and float. In addition, some jellyfish umbrellas have air bags on the top. These jellyfish control the amount of inflation in each air bag and can also change the direction of the jellyfish's movement.

The body of a jellyfish is shaped like a transparent umbrella, with diameters ranging from large to small.

The umbrella body of ordinary jellyfish is not very large, only 20-30 centimeters long, while the diameter of the umbrella body of large jellyfish can reach 2 meters. Some baleen-like strips grow from the edge of the umbrella body. These strips are called tentacles. Some of the tentacles can be 20 to 30 meters long, which is equivalent to the length of a large whale. Jellyfish floating in the water extend their long tentacles around, and some jellyfish have various patterns on their umbrellas. In the blue ocean, these swimming elves of different colors look very beautiful. In 1865, on the coast of Massachusetts, the United States, a rosy jellyfish was washed ashore by the waves. Its umbrella diameter was 2.28 meters, and the tentacles are 36 meters long. Pulling the tentacles of this jellyfish apart, it is 74 meters long from the tip of one tentacle to the tip of the other. Therefore, it can be said that the jellyfish is the longest animal in the world.

Toxic

Jellyfish are beautiful but ferocious. Under the umbrella, those slender tentacles are its digestive organs and also its weapons. The tentacles are covered with stinging cells, which are like poisonous threads and can shoot venom. After the prey is stung by the stings, it will be quickly paralyzed and die. The tentacles grab these prey tightly, retract them, and use the polyps under the umbrella to suck them. Each polyp can secrete enzymes to quickly break down the protein in the prey. Once a jellyfish encounters its prey, it never lets it go easily. When you are stung by a jellyfish and have difficulty breathing, you should immediately implement artificial respiration or inject cardiotonic drugs. Do not be careless to avoid accidents.

In the hot summer, when people swim in the tide at the beach, they sometimes feel a sudden tingling sensation in the chest, back or limbs of the body, which feels like being whipped by a whip. It's the jellyfish that's stinging people. However, when stung by a jellyfish, you will generally feel pain and redness and swelling. As long as you apply anti-inflammatory drugs or vinegar, the swelling and pain will subside in a few days. However, on the sea surface from Malaysia to Australia, there are two types of jellyfish called trailing hand jellyfish and box jellyfish (or sea wasps), which secrete highly toxic substances.

Mighty and deadly jellyfish also have natural enemies. Leatherback turtles can freely shuttle among the jellyfish groups and easily tear off their tentacles with their mouths, causing them to roll up and down, and finally lose their ability to resist. , becoming a "good meal" for sea turtles.