The méduse, commonly known as the jellyfish, is a marine creature found in oceans worldwide. It has a soft, gelatinous body, typically shaped like an umbrella, with tentacles that hang down. These tentacles contain specialized cells called nematocysts, which can sting and capture prey, such as small fish and plankton. Jellyfish are part of the phylum Cnidaria, which also includes corals and sea anemones. They have existed for millions of years and can vary in size, from a few centimeters to over two meters in diameter. Despite their simple structure, jellyfish play a crucial role in marine ecosystems.