Ch. 34 Platyhelminthes (phylum) Flatworms –Lacks circulatory system –Lacks respiratory system –Bilateral symmetry –Senses and nerves at the anterior end called cephalization. Three classes: Turbellaria, Trematodes, Cestoda. Video Clip

Turbellaria (class) Planaria is an organism in this class. 1. Its freshwater 2. Swims with the aid of cilia 3. Its mouth is in the middle of its body. It extents out by a tube called the pharynx. 4. Water and wastes are exited out the planaria through the flame cells.

5. Planaria have the ability to sense light with 2 anterior eyespots. 6. Planaria have 2 anterior nerve cells called ganglia. The ganglia enables the planaria to sense touch, taste, and smell. It is much like a simple brain. 7. Planaria are hermaphrodites. 8. Planaria are able to regenerate.

Trematoda (class) Flukes (hosts) –Endoparasites – live inside the host –Ectoparasites – live on the external surface of the host. Video Clip`Video Clip

Lifecycle of the liver fluke –Mates inside the liver of a sheep. Eggs enter the intestine and exit. Eggs hatch in water and invade snails as larva form. The larva leave the snails as a free swimmer and form a cyst on grass blades on land. The sheep eat the grass and the cyst hatches in the digestive tract and bore there way into the blood system which leads them to the liver.

Cestoda (class) Tapeworms 1. Parasitic just like flukes. 2. Lack sense organs, mouth, and digestive system 3. Attaches to a host with its hooks and suckers. 4. Head is called scolex. Body segments are called proglottids. Video Clip

Nematoda (phylum) Roundworms –1 mm to 120 cm –Parasites in digestive tract –2 openings – mouth and anus Trichinosis occurs in humans. Become infected by eating undercooked pork with trichina cysts. Causes pain and stiffness as a cyst in muscle cells. Freeze pork for 72 hours.