The Hydra is a tiny tentacled creature with no eyes or brain. Named after the Lernean Hydra from Greek legends, Hydra vulgaris has a morphallactic regenerative capability-the ability to regenerate specific tissues that are lost or need replacing-that seems to keep them from aging or dying.
This episode of Deep Look from KQED explores how the mysterious hydra replaces all of their cells every 20 days. From the transcript:
They can do that because roughly half of the cells in their bodies are stem cells, which can develop into all the different types of specialized cells you need to build or rebuild a body.
Stem cells only make up a tiny percentage of our bodies. And our stem cells degrade over time — that’s why we age. But a hydra can make near-perfect copies of its stem cells … basically forever.
It’s called non-senescence — biological immortality. Having all those stem cells allows hydra to recover from all kinds of … damage.
The video includes an experiment that tests this by cutting the organism in half. Deep Look also shares ultraviolet light footage that reveals how the hydra’s exterior and interior cells can reorganize and rebuild themselves after being mixed up.
Related reading at UC Davis: Mapping Cells in the “Immortal,” Regenerating Hydra.