1. Body Cavities  What is between the body wall and the gut?  The simplest animals have this regions packed with body organs, but more complex animals have a cavity separating the body wall from the gut. These are known as acoelomates.  If this cavity has a lining that holds the internal organs in place, it is called a “coelom”.  Some animals have the cavity without a lining. This condition is called “pseuodcoelomate”.

3. Acoelomate Bilateral Animals  Unlike the radiate animals all of these organisms are mobile and have evolved cephalization with their sense organs concentrated at the head end. There is also the beginning of a ladder-type nervous system.  In addition, they are bilaterally symmetrical.

4. Platyhelminthes –Flatworms (“platy”-flat, “helminth”-worm)  Bilateral Symmetry (L/R, A/P, D/V)  Has three official layers (Endoderm  gastrodermis, Mesoderm  muscles, Ectoderm  epidermis)  Acoelomates – no body cavity (lack of cavity makes being ‘flat’ important – no cell can be too far from outside!)

5. Feeding  Still only ONE opening to dig.tract!  Free living(scavengers) or parasitic (specialized structures, usually with hooks or suckers, to attach to host)  Gut is highly branched, to get food to all parts of body!

6. Respiration & Excretion  Excretion - Flame cells remove excess water  Respiration - Oxygen diffuses directly into body cells

7. Nervous Systems  First appearance of cephalization (concentration of sensory “organs” at anterior end)  Primitive brain, coordinates muscle activity with various types of “nerve ladders”

8. Flatworm Anatomy

9. Reproduction  Sexual – Hermaphrodites. Internal fertilization, some require cross- fertilization (sperm exchange), some can self fertilize.  Some engage in ‘penis fencing’  Asexual – fission (will pinch in two)  When damaged, regenerates new body parts.

10. Free Living Class Turbellaria (planarians)  Ex. Common Planaria (Dugesia sp.)  Good movement (muscles coordinated by nerve ladder; cilia)  Sense organs - eyespots, auricles (“false ears”)  “Tummy Tube” (pharynx), branching digestive cavity to reach all parts of body

11. Parasitic Class Cestoda (Tapeworms)  Ex. Beef Tapeworm (Taenia sp.)  Hooks and Suckers to hang on…  Reduced sense organs (don’t need ‘em!)  Great reproductive system! Lots of tough eggs in Proglottids…

12. Beef Tapeworm Life Cycle Adult tapeworms infect the small intestines eggs released in feces Attach to vegetation Ingested by cows; encyst in muscles people

13. Parasitic Class Trematoda (Flukes)  Ex. Chinese Liver Fluke (Clonorchis sp.)  Suckers to hang on to bile ducts…  Complex life cycle; two intermediate vectors (hosts)

14. Chinese Liver Fluke Life Cycle Adult flukes infect liver and gall bladder eggs released in feces Ingested by snail Miracidium, sporocyst, redia, cercaria Fish people Currently infect an est. 30,000,000 people!