Jellyfish or jellies are the major non-polyp form of individuals of the phylum Cnidaria. They are typified as free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles
Jellyfish, or Scyphozoans, have no structures dedicated for respiration or circulation. However, they still need oxygen, just like every other animal. They do have several physiological adaptions that allow them to take up oxygen, and even store it, allowing jellyfish to survive in low-oxygen conditions.