Your first reaction to the following video will probably be that it’s a fake.
But no, it’s totally real. The mudfish they’re talking about are called West African Lungfish and they’re one of four African lungfish species. And they can indeed live in the desert, inside a cocoon, for up to five years. And yes, they do have to appendages at the back that look kind of like legs. Even crazier, they can breathe air, because they have — in addition to gills, and as the name suggests — an actual lung.
What happens is that the West African weather has wild rain swings between wet and dry seasons (and sometimes there are droughts), so entire rivers can dry up. When the lungfish end up on a dry riverbed, they’re still ok, because they switch to breathing air. Then they burrow into the mud, before it dries up, by eating the mud and excreting it through their gills. Once they’re safely underground, they curl up and release a mucus that dries up around them to form that cocoon from the video, which basically Ziplocks them in, so they don’t lose any more moisture. They then enter suspended animation, which is called aestivation. It’s basically the same thing as hibernation, but while that happens when it’s too cold out, this happens when it’s too hot out.
They can remain in aestivation for years, until it starts raining again and the river beds fill up with water, softening the cocoon and allowing the lungfish to burrow out of the mud and get back into the water. The African people have gotten pretty good and finding the cocoons and sometimes they dig them up and store them, so they can have fresh fish at their disposal.