MCQ Detailed View

Leeches are fascinating invertebrates belonging to the phylum Annelida. They are closely related to earthworms but have unique features, especially in their nervous system. The question of how many brains a leech has often surprises students, because the answer is not one brain but 32 brains.

In a leech, the nervous system is composed of a series of ganglia, which are clusters of nerve cells. These ganglia function like mini-brains, controlling different parts of the body. A leech has a total of 32 segments, and each segment contains its own ganglion. Together, these ganglia form a chain-like structure along the body. This arrangement is why scientists often say that a leech has 32 brains.

The first ganglion in the head region acts as the central control center, similar to a true brain, but each additional ganglion has enough nerve cells to independently coordinate movement and responses in its own segment. This is why, even if part of the leech is separated, that section can still respond to stimuli for some time.

This distributed nervous system gives leeches excellent coordination and flexibility. It allows them to move smoothly, attach to hosts, and respond quickly to changes in their environment. The system also helps them survive injuries, since control is spread across multiple ganglia rather than concentrated in a single brain.

It is important to note that while we say “32 brains,” they are not full brains like in humans. Instead, they are segmental nerve centers that collectively manage the body. This unique adaptation makes leeches an interesting subject of study in biology and neuroscience.

Thus, the correct answer is 32, highlighting the remarkable way evolution has shaped the nervous system of these simple but specialized creatures.