A hydra is a tiny animal, roughly half an inch in length. Although biologists have known about them for a long time, they were uncertain how these miniscule creatures open their mouths.

Now, researchers have discovered the process by which hydras ingest food – they tear apart their own bodies at each meal.

Hydra attach one end of their tube-like bodies to a rock or other outcropping in the water, where they wait for prey to come within striking distance. When a shrimp or other tiny marine animal brushes against the tentacles of the hydra, tiny barbs shoot out, stinging the wanderer. The stingers then contract, drawing the prey into the throat of the stationary hunter.

Following digestion, the mouth opens once more to expel waste products, before the organ is once more sealed with body tissue. This much of the process has been well-understood for quite a while, although scientists were unaware of the process by which the mouth actually opened at the start of the process.

However, before this can happen, the freshwater animals must rip apart their bodies in order to open their mouths, new research reveals. Examination revealed the entire process of a hydra tearing apart its body to open its mouth takes around 60 seconds to complete.

Hydra vulgaris was genetically modified so that both layers of skin glowed for easy observation. They found the mouth of the creatures opened in much the same way as the pupil of a human eye when exposed to darkness. When biologists exposed the creatures to muscle relaxants, they were unable to stretch open their mouths.

"The fact that the cells are able to stretch to accommodate the mouth opening, which is sometimes wider than the body, was really astounding. When you watch the shapes of the cells, it looks like even the cell nuclei are deformed," Eva-Maria Collins from the University of California, San Diego said.

Hydras are well-known for their ability to repair damage after their bodies are ripped apart. Now, biologists have learned how that ability serves the creatures during feeding. Researchers hope to learn more about the process of tissue formation by studying the feeding pattern of the tiny marine animals.

Analysis of how hydras rip their bodies apart in order to feed was profiled in the Biophysical Journal.