Like all jellyfish, the immortal jellyfish begins as a larva (planula) that develops from a fertilized egg. At first, a planula swims, settling on the seafloor, and growing into a cylindrical colony of polyps. The immortal jellyfish grows to adulthood in a matter of weeks, and a fully grown adult is only about 0.18 inches across, smaller than a pinky nail. It has a transparent bell, with edges lined up with up to 90 white tentacles.

Though small, the transparent immortal jellyfish has extraordinary survival skills. When they face starvation or experience physical damage, they respond by transforming into a polyp. In this remarkable process, the born-again polyp buds and releases medusae that are genetically identical to the adult.

In a rare process called transdifferentiation, the immortal jellyfish can revert back to a polyp when faced with starvation or injury. An adult cell specialized for a tissue becomes a specialized cell. In a way, it's an efficient way of cell recycling. The immortal jellyfish can succumb to predation or disease while still in the medusa stage.

Fun Facts

• The immortal jellyfish was first discovered in the Mediterranean Sea in the 1880s and was identified as a uniquely enduring organism.
• A fully grown immortal jellyfish is only about 4.5mm (0.18 inches).
• The jellyfish has a bright red stomach in the middle of its transparent bell; the edges of the bell have up to 90 white tentacles.
• The immortal jellyfish takes just a few weeks to grow to adulthood.
• The immortal jellyfish have been known to hitch rides in the ballasts of ships.