Common Hydra

• biologíaIt shows no detectable biological sign of ageing and can regrow its whole body from a small fragment of tissue.
• It regenerates a complete individual from a minute fragment of its body, a capacity Abraham Trembley demonstrated in 1744, causing a philosophical shock in Enlightenment Europe.
• It moves by somersaulting: it bends over, fixes its tentacles, releases its base and plants it again further on.
• It appears not to age. Under laboratory conditions its mortality and reproduction rates do not rise over time: an eight-year study found no sign of senescence, and it has been estimated that 5 % of a cohort would still be alive after 1,400 years.
• The reason lies in its stem cells: it renews its entire body continuously, so that no tissue ever grows old.
• It regenerates a complete individual from a tiny fragment, something Abraham Trembley demonstrated as early as 1744 by cutting it to pieces, one of the founding experiments of developmental biology.
• It reproduces mainly by budding: a daughter hydra sprouts from its side, detaches and goes on alone.
• It has neither a brain nor a centralised nervous system, only a diffuse nerve net, and yet it actively hunts small crustaceans with its tentacles.

Habitat & environment

Submerged vegetation of freshwater ponds, lakes and backwaters

Sources consulted: Pallas (1766); Trembley (1744); Schaible et al. (2015), PNAS; Martínez (1998)