The goopy puddles known as slime molds are part of a group of microbes called protists. These single-celled organisms don't have brains, yet researchers discovered they have memories.
Slime molds secrete a thick, translucent slime as they move. Then, they use the slime trail they've laid down to record where they've been -- which, in turn, helps them go around obstacles and find things. In studies, researchers hid a sugary meal behind a U-shaped barrier, and the slime mold found it by using its trail to figure out where it had already been, and thus where to look next [source: Choi].
Such a memory isn't the same as a human memory, of course. Slime molds can't store memories, for example. Still, the findings help us understand how early organisms figured out problems and puzzles. And the discovery marks the first demonstration of a spatial memory system in a brainless organism [source: Choi].