1. Phylum Platyhelmenthes Planarians, Flukes, & Tapeworms
Simple acoeleomates
Bilaterally symmetrical
Most flattened "Dorsoventrally"
Divided into 4 classes:

2. Class Turbellaria Most free-living and non parasitic
Include planarians
Lack circulatory and gas-exchange organs.
Simple excretory structures called flame cells that maintain osmotic balance.
Is cephalized and has eye-spots which are sensitive to light
Feeds through ventral feeding tube called a pharanx
Can reproduce sexually, or asexually through regeneration

3. Planarian and assorted marine flatworms…

4. Class Trematoda (Flukes)
Similar in form to turbillarians
Many are parasitic. Example of parasitic fluke is the asian liver fluke
Many have complex life cycles including multiple hosts and alternation of generations.

5. Life Cycle of the Liver Fluke

6. Liver Flukes Cont’d…
Liver Fluke
Liver Fluke encysted in a liver

7. Class Cestoda (Tapeworms)
Parasitic flatworms
Can grow to enormous lengths (up to 20m)
Parasitize mostly vertebrate hosts
Attach head named scolex to intestinal walls of host, and abosrb host's nutrients
Following scolex is a series of repeating structural units called proglottids
Mature proglottids containing thousands of eggs are released with the host's feces to infect other organisms.

8. Tapeworms cont’d…