Jellyfish, also known as medusae, bud off these polyps and continue their life in a free-swimming form. Eventually they become sexually mature. All the polyps and jellyfish arising from a single planula are genetically identical clones.
Turritopsis dohrnil is a species of jellyfish that apparently does not die of natural causes, because it can revert to the juvenile stage from the adult stage. However, it is not actually immortal. Most Turritopsis are likely to be eaten by predators or die from disease in the adult stage.
- WoRMS 2012. P. Schuchert (ed) Turritopsis dorhnii (Weissmann, 1883). World Hydrozoa database. World Register of Marine Species. 
- Bavestrello, Giorgio; Christian Sommer; Michele Sarà (1992). "Bi-directional conversion in Turritopsis nutricula (Hydrozoa)". Scientia Marina 56 (2–3): 137–140.
- Piraino, Stefano; F. Boero; B. Aeschbach; V. Schmid (1996). "Reversing the life cycle: medusae transforming into polyps and cell transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa)". Biological Bulletin (Biological Bulletin, vol. 190, no. 3) 190 (3): 302–312. doi:10.2307/1543022.
- Ker Than (January 29, 2009). ""Immortal" jellyfish swarm world's oceans". National Geographic News. Retrieved 2010-06-16.
- S Kubota (2011). "Repeating rejuvenation in Turritopsis, an immortal hydrozoan (Cnidaria, Hydrozoa)". Biogeography 13: 101–103. ISSN 1345-0662. http://www.benikurage.com/jp/2011biogeography.pdf.