meduse

Meduse, the French term for jellyfish, refers to gelatinous, umbrella-shaped marine animals in the phylum Cnidaria. In biology, the term medusa also denotes the free-swimming sexual stage of many cnidarians, in contrast to the sessile polyp stage.

Medusae belong mainly to the classes Scyphozoa, Cubozoa, Hydrozoa, and Staurozoa. They typically have a bell- or umbrella-shaped body with trailing tentacles or oral arms that contain specialized stinging cells called nematocysts. They move by rhythmic contractions of the bell, which allows drifting or slow propulsion, and they feed on small planktonic organisms, larvae, and other tiny prey.

Most medusae reproduce sexually. In the common jellyfish life cycle, a free-swimming medusa releases gametes into the water, fertilization yields planula larvae that settle as polyps. Some hydrozoans also reproduce asexually by budding polyps, which can later produce medusae through a process called strobilation.

Jellyfish occur in oceans worldwide, from coastal zones to the open sea, and a few species tolerate brackish water or freshwater. They play roles as both predators and prey within marine ecosystems. Encounters with humans can result in stings that range from mild irritation to severe envenomation, depending on species and conditions. Medical attention is typically advised for painful or widespread stings, particularly from highly venomous species.