Jellyfish is a very beautiful aquatic animal. Although it has no spine, its body is very huge, mainly supported by the buoyancy of water. The jellyfish body looks like a transparent umbrella, and the diameter of the umbrella is large or small. The diameter of the umbrella of the big jellyfish can reach 2 meters. There are some whisker-like strips on the edge of the umbrella, which are called tentacles. Some tentacles can be as long as 20 to 30 meters, which is equivalent to the length of a big whale. Floating around with long tentacles, the umbrella-shaped bodies of some jellyfish also have various patterns. In the blue ocean, these swimming jellyfish of different colors look very beautiful. The appearance of jellyfish predates dinosaurs and can be traced back to 650 million years ago. At present, there are about 200 species of jellyfish found in the world, and there are about 8 common species in China, namely, Haiyue jellyfish, Baixia jellyfish, jellyfish and crested jellyfish. The tentacles of jellyfish are covered with stinging cells. This stinging cell, like a small bean stuck on the antenna, can emit poisonous filaments. When it meets an "enemy" or prey, it will emit poisonous filaments to scare off the "enemy" or poison it. There is a small ball on the slender handle in the middle of the jellyfish tentacles, which is the "ear" of the jellyfish. Scientists have simulated the sound wave transmitting organs of jellyfish and found that they can be used in the ocean.

Although jellyfish are beautiful and comfortable in water, they can't live without water. The water content of jellyfish is 98%, so it can only be eaten, digested and excreted in water. Without water, jellyfish's body will become smaller and uglier. Jellyfish is more dangerous than cobra. A few years ago, the American World Wildlife magazine listed 10 kinds of the most poisonous animals in the world according to the opinions of scholars from all over the world. At the top of the list is the box jellyfish that lives in the ocean. Box jellyfish, also known as sea wasp, is a coelenterate, mainly living in the coastal waters of northeast Australia. Adult box jellyfish are as big as football, mushroom-shaped and almost transparent. An adult box jellyfish has billions of poison sacs and needles on its tentacles, enough to kill 20 people, and its toxicity is obvious.