There are more than 200 species of jellyfish in the world's oceans. They are distributed in waters all over the world, whether it is tropical waters, temperate waters, shallow waters, oceans about 100 meters deep, and even freshwater areas.
Jellyfish have existed since the Ediacaran period. Jellyfish come in different shapes and sizes, with the largest tentacles extending about ten meters. In terms of classification, some belong to the class of Hydra, and some belong to the class of jellyfish.
The life cycle of jellyfish is very complex, with different lifespans, and related research is also relatively lacking. The most special is the lighthouse jellyfish (scientific name: Turritopsis nutricula), which can achieve "immortality" through repeated normal reproduction and transdifferentiation.
All jellyfish are carnivores and they feed on fish and plankton. When hunting, jellyfish are passive and only prey on animals that swim to them. They use the nematocysts on their tentacles to sting or kill their prey, and then deliver the food to their mouths and digestive cavities. Most jellyfish are almost transparent, making them difficult for enemies to spot. Some jellyfish are capable of glowing, and just by the dim light on their bodies, jellyfish can attract prey without much effort.
