Jellyfish larva. Coloured scanning electron micrograph (SEM) of a stage in the larval development of a jellyfish. Jellyfish are any of numerous usually free-swimming marine coelenterates of the class Scyphozoa, characteristically having a gelatinous, tentacled, often bell-shaped medusoid stage as the dominant phase of its life cycle. This immature medusa or ephyra was found in a sample of zooplankton, the array of microscopic animals found floating in the world's oceans. Magnification: x250 when printed at 10 cemtimetres across.