水母, commonly known as jellyfish, are gelatinous marine animals found in oceans worldwide. They belong to the phylum Cnidaria and are characterized by their umbrella-shaped bell and tentacles. Jellyfish can vary in size, from a few centimeters to over two meters in diameter, and they are known for their unique ability to drift with ocean currents. Jellyfish have a simple body structure, lacking a brain and heart. They primarily feed on small fish, plankton, and other marine organisms by using their tentacles, which contain specialized cells called nematocysts to capture prey. Some species of jellyfish can also produce bioluminescence, creating a beautiful glow in the water.