Turritopsis dohrnii

Turritopsis dohrnii is a small hydrozoan jellyfish that can revert from its adult medusa stage to a juvenile polyp stage, potentially repeating its life cycle.

Transdifferentiation: A process in which a differentiated cell changes directly into another cell type. Cellular reprogramming accompanies the medusa-to-polyp transformation.
Hydrozoa: A class of cnidarians that includes hydroids, siphonophores, and many small jellyfish. Turritopsis dohrnii belongs to this diverse cnidarian class.
Turritopsis nutricula: A hydrozoan jellyfish historically confused with Turritopsis dohrnii in reports of life-cycle reversal. Older claims about an immortal jellyfish often concerned this different species.
Regeneration (biology): The regrowth or reorganization of tissues and body structures after damage or loss. Its life-cycle reversal is a striking form of whole-body reorganization.
Biological immortality: A condition in which mortality risk does not rise with age, distinct from being impossible to kill. Life-cycle reversal inspired the label, but the jellyfish remains vulnerable to disease, predation, and other hazards.
Hydrozoan life cycle: A life cycle in many hydrozoans that alternates between polyp and medusa forms. Turritopsis dohrnii reverses a stage in this broader life-cycle pattern.
Cnidaria: A phylum of mostly aquatic animals with stinging cells, including jellyfish, corals, and sea anemones. Its defining stinging cells place this species within the phylum.
Turritopsis rubra: A species of Turritopsis found in the southwestern Pacific region. It is a close relative that helps place dohrnii within its genus.
Cellular reprogramming: A change in a cell’s gene-expression state that alters its identity or developmental potential. The reversal prompts investigation into how mature tissues regain earlier developmental states.
Aging in cnidarians: The study of age-related change across cnidarian species and life stages. Comparisons test whether reversal corresponds to reduced or altered aging.

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