Monday, February 26, 2007


phylum Platyhelminthes
Nervous systems of free-living flatworms allow them to gather information from their environment. Free-living flatworms have well-developed nervous system than cnidarians and sponges. Flatworms are capable of simple learning and can sense taste, smell, touch, and light. Free-living flatworms have a brain, a control center of a simple nervous system, located in the anterior end. Long nerve cords stretches throughout the body from the anterior end to posterior end. Many flatworms have light sensitive organs called ocelli, or eyespots. Flatworms also have cells that are sensitive to chemicals found in food, and other cells that tell the worm which way the water around them is flowing.
Parasitic flatworms do not have much of nervous systems because they live in their host and absorb food from intestinal walls.

★The eyespots do not help flatworms to see objects; however, they detect whether the animal is in light or in darkness.

phylum Nematoda
Roundworms have simple nervous systems. They contain ganglia, or groups of nerve cells, in the head region. Roundworms have sensitive organs that detect chemicals given off by hosts. Nerves stretch from the ganglia at the head region to the posterior part of the body. These nerves transmit sensory information and control movement.

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