Scyphozoans (an alternative name: the True Jellyfish) are marine invertebrates, and can be found in every ocean in the world, and contains about 200 species. They have no head and no special organs for respiration or excretion. They do not have a rigid skeleton nor any specialized organ systems. Scyphozoans typically range from 2 to 40cm (0.79 to 16in) in diameter. True jellyfish are graceful, and sometimes deadly creatures. Their stings may cause skin rashes, muscle cramps, or even death.