Hydras are tiny animals that live in freshwater. Just by looking at them (and their many tentacles), you can probably guess their closest relatives: jellyfish, sea anemones, and corals. Scientists have long known that hydra mouths can open wider than the diameter of their bodies, which is impressive in itself. What's truly strange is that hydras don't have permanent mouths. Each time they open their mouth, they're essentially tearing a new hole in their flesh. Upon closing, the mouth is sealed with intercellular junctions in a process that has been compared to "healing a wound."
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Key Facts In This Video
Hydras are freshwater animals that typically measure less than an inch long. 00:10
Hydras rip holes in their own sealed tissue to create a mouth when they eat. 00:35
When a hydra opens its mouth, its cells do not rearrange, but instead stretch and reform dramatically. 01:15
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