Jellyfish are simple marine animals known for their gelatinous, umbrella-shaped bodies and long, trailing tentacles. They belong to the phylum Cnidaria and can be found in oceans worldwide, from shallow coastal waters to the deep sea. Jellyfish are mostly composed of water, making them appear translucent and delicate. These creatures use their tentacles to capture prey, primarily small fish and plankton, by delivering a sting through specialized cells called nematocysts. Jellyfish have a unique life cycle that includes both a polyp stage and a medusa stage, allowing them to reproduce both sexually and asexually.