


Do Flatworms Have a Brain?

By Sarah Whitman

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There are many different species of flatworms. Some of the more common species, such as Procotyla fluviatilis, can grow up to almost an inch in length and are often brown or greenish in color. Flatworms do have brains, which are not only able to learn, but regenerate and remember previous actions.

Flatworm Information

Flatworms, also known as planarians, live in shallow bodies of water including lakes, streams and ponds. Flatworms are not close relatives of other worms and differ in appearance. For example, their bodies are flat, not round like other worms, and their bodies have no segments. Although they live in the water, they cannot swim, opting instead to glide across layers of mucus they produce themselves. About 80 percent of flatworms live as parasites on other organisms.

Flatworm Brains 101

Flatworms are the simplest animal to possess a symmetrical body and a system of cephallization, a term used to describe the sensory network of the head and brain. The flatworm brain contains two lobes, along with a nerve cell-containing cortex and a base of nerve fibers. The planarian brain is also equipped with the presence of neurotransmitters, chemical substances released by nerve fibers and associated with people's perceptions and moods such as happiness and sadness.

They Have Eyes, Too

Flatworms also have eyes, which have a working connection with the brain. Their eyes are sensitive to light, and they choose to stay in dark, shady or underground areas during the day. Their eyes can also follow light's direction.

Evolutionary Precedence

The flatworm is likewise sensitive to other environmental stimuli and impositions, including toxins. The flatworm evolved before vertebrates and is therefore considered one of the earliest evolutionary examples of a brain. This status offers researchers and others a glimpse into the early brain.

Retention of Memories

Flatworm bodies have amazing ability to regenerate. This is thought to be a result of the large percentage of stem cells in their bodies. Researchers from Tufts University trained flatworms to tolerate light and open spaces, both usually avoided. About 10 days later, after the worms learned to retrieve food from an open dish surrounded by light, researchers decapitated them. Two weeks later, the brains not only grew back, but the worms retained most of the memory of their prior feeding routine.

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