Turritopsis

Turritopsis is a genus of small hydrozoan jellyfish in the family Oceaniidae. It includes several species, with Turritopsis dohrnii being the best known. Members of this genus are tiny, transparent medusae that inhabit warm temperate and tropical seas. They are often found in coastal environments such as harbors, reefs, and pilings, and may be transported by ships in ballast water.

A distinctive feature of some Turritopsis species, particularly T. dohrnii, is the ability of mature medusae to revert to an earlier developmental stage. Through a process known as transdifferentiation, cells can transform into different cell types, allowing a medusa to regress to a polyp stage and then re-grow into new jellyfish. This has led to the popular notion of an “immortal jellyfish.” In nature, this reversal is not guaranteed and is typically triggered by environmental stress; even so, individuals can still die from disease, predation, or unsuitable conditions.

The life cycle of Turritopsis generally involves sexual reproduction in the medusa stage, producing planula larvae that settle as polyps. Polyps can reproduce asexually by budding to form new medusae, thereby maintaining local populations. The genus contains several species, and taxonomic definitions have been subject to revision and debate, with some confusion between T. dohrnii, T. nutricula, and related forms.

In research, Turritopsis has attracted interest for studies of cellular plasticity and regeneration. Its unusual life-history traits provide insight into developmental biology and aging, though claims of true immortality are overstated and context-dependent.