Jellyfish or jellies are softbodied, free-swimming aquatic animals with a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate to acquire propulsion and locomotion. The tentacles may be utilized to capture prey or defend against predators by emitting toxins in a painful sting. Jellyfish species are classified in the subphylum Medusozoa which makes up a major part of the phylum Cnidaria, although not all Medusozoa species are considered to be jellyfish. from wiki