The Hydra Rips Its Face Open Every Time It Eats, Then It Heals Its Mouth Shut

A hydra vulgaris with 6 tentacles. Corvana/Wikipedia

Hydra vulgaris is a small, boneless freshwater creature less than half an inch long. It might not look special, with its four to 12 tentacles dangling in the water, waiting for a tasty micro shrimp to pass by, but it has been an object of fascination for scientists for decades because of its impressive ability to regenerate itself.

If you cut a hydra in two, both parts will turn into smaller hydras thanks to a phenomenon called morphallaxis. With an ability like this, it’s not surprising that it was named after a Greek mythology figure, the nine-headed serpent-like Hydra which grows back two heads for every one that is cut off.

Creepy, but effective

The real hydra uses its regeneration abilities in a very unusual way to feed itself, and for the first time, biologists have been able to understand what’s really going on. Their findings were published in the latest Biophysical Journal. It turns out that the hydra basically rips its own skin open every time it needs to open its mouth, and then rapidly heals the torn-up tissue. Another way to look at it is that it doesn't have a mouth except when it needs one. This might sound like a horror film scenario, but the event is not dangerous for the small creature thanks to its ability to heal very rapidly.

You can see it take place in the video above, which was created by UC San Diego biophysicists to show how the hydra tears a hole in its epithelial tissue each time it opens its mouth. The green and purple colors appear because the scientists color-tagged proteins in ectodermal and endodermal epithelial cells to better see what goes on at the cellular level when a hydra feeds.

“It’s fascinating that Hydra has to tear a hole every time it opens its mouth,” said Eva-Maria S. Collins, an assistant professor of biology and physics at UC San Diego who headed the research team. “And that this process happens so quick; this was the first indication to us that mouth opening did not involve cellular rearrangements.”

The methods used to study the hydra’s mouth will be useful to study tissue formation and patterning in all kinds of other organisms. Some medical breakthrough in humans might come from a tiny creature that has to create itself a new mouth with every bite.