Which animals have 32 brains?

The Surprising Anatomy of Leeches: 32 Brains and Counting

It sounds like something out of science fiction—animals with 32 brains. But for leeches, this is reality. These small, segmented creatures, often found in freshwater environments, possess a decentralized nervous system that functions as 32 separate ganglionic "brains" distributed along their bodies. Each segment of the leech has its own cluster of nerve cells, allowing for remarkable coordination and movement, even when parts of the body are damaged.

Beyond their multiple brains, leeches boast a suite of unusual features. They have five pairs of eyes, giving them a total of ten—though their vision is limited and mostly used to detect light and shadows. Their mouthparts are equally impressive: a set of sharp jaws lined with about 300 tiny teeth, which they use to make a small incision when feeding. Unlike mammals, leeches don’t rely on a single stomach. Instead, they have 10 stomach-like compartments arranged in a row, allowing them to store large amounts of blood—sometimes up to five times their body weight—in a single feeding.

Despite their creepy reputation, leeches have played a vital role in medicine for centuries. Historically used in bloodletting, they are now valued in modern surgery for their ability to promote circulation, especially in reattached limbs or skin grafts. Their saliva contains anticoagulants and anti-inflammatory agents that help prevent clotting and reduce swelling.

So, while leeches may seem simple at first glance, their complex anatomy reveals a highly evolved creature built for survival. With 32 brains, 10 stomachs, and a suite of other adaptations, they’re a fascinating example of nature’s ingenuity.