Roundworms
Roundworms have simple nervous systems. They have several ganglia, or groups of nerve cells in the head region, but they lack anything that can really be called a brain. Although roundworms have several types of sense organs, these are simple structures that detect chemicals given off by prey or hosts. Several nerves extend from the ganglia in the head and run the length of the body. These nerves transmit sensory information and control movement. The muscles of roundworms run in strips down the length of their body walls. Aquatic roundworms contract these muscles to move like snakes through the water. Soil-dwelling roundworms simply push their way through the soil by thrashing around.
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Nervous System