1. PLATYHELMINTHES Eumetazoa: Bilateria: Phylum Platyhelminthes (flatworms) marine, freshwater, terrestrial

2. PLATYHELMINTHES either Protostomia or Lophotrochozoa triploblastic: 3 germ layers ectoderm: epidermis, nervous tissue mesoderm: true muscle tissue endoderm: gastrodermis lining gastrovascular cavity acoelomate

3. PLATYHELMINTHES lack some organ systems (circulatory, respiratory) diffusion: reason why small and flat have others (muscular, nervous, digestive, excretory, reproductive) nervous system (Fig. 49.2): eye spots, rudimentary brain, nerve cords cephalization (head); Fig. 33.10, Fig. S4-2

4. PLATYHELMINTHES hermaphroditic: male and female reprod. systems in same individual adaptive advantage: every individual potential mate digestive system: mouth, pharynx, gastrovascular cavity one way gut; no anus invagination: increases surface area

5. PLATYHELMINTHES excretory system: protonephridia (Fig. 44.11); proto = first, nephrus = kidney branching network of tubules flame-bulb cell with cilia draws mostly water, some waste into tubules exit via nephridiopores

6. PLATYHELMINTHES free-living (non-parasitic) ancestral life history many parasitic in vertebrate gut suckers/hooks; Fig. S4-3 reduce/lose some ancestral characters tapeworms: no mouth/gastrovascular cavity/excretory structures; diffusion mostly reproductive organs Fig. 33.12

7. MALFORMED FROGS mystery of the malformed frogs August 1995: school kids in MN, field trip to a pond; amphibian malformation

8. MALFORMED FROGS most states, range of deformities hypothesis: endocrine disrupting chemicals disrupt development by disrupting hormones

9. MALFORMED FROGS alternative: trematode hypothesis trematodes (= flukes) Ribeiroia life cycle: encysts in limb buds

10. MALFORMED FROGS can cause deformities, but why now? human-caused ecosystem disruption nutrient runoff: organic pollution (fertilizer, manure, sewage) increased snail population (a key host) modified hypothesis: nutrient-trematode

11. NEMATODA Eumetazoa: Bilateria: Phylum Nematoda (roundworms)

12. NEMATODA Protostomia or Ecdysozoa pseudocoelom complete digestive tract (2 openings) hangs free in pseudocoelom; Fig. S5-1 cylindrical, unsegmented body cuticle: tough, thick outermost layer around epidermis; ecdysis

13. NEMATODA hydrostatic skeleton: fluid in pseudocoelom; high pressure nervous system: anterior nerve ring, dorsal/ventral nerve cords no circulatory/respiratory systems; diffusion muscular system: longitudinal muscle locomotion: contraction; thrashing

14. NEMATODA only sexual reproduction (Fig. S5-2) some hermaphroditic, others dioecious dioecious: separate male, female reprod. system fills most of organism

15. NEMATODA free-living (soil); parasitic uniform structurally, diverse ecologically species differ in specific habitat probably over one million species: speciose 1 sq m of marine mud: 4.5 million individuals!; very successful much to be learned

16. NEMATODA Caenorhabditis elegans (C. elegans) model organism free-living soil nematode; easy to raise transparent; life cycle: 3½ days every cell mapped, fate known; Fig. 47.22

17. C. elegans entire genetic sequence known huge medical applications humans, nematodes both bilaterians evolutionary medicine: studying other organisms for insight into humans

18. ANNELIDA Eumetazoa: Bilateria: Phylum Annelida (segmented worms) Protostomia or Lophotrochozoa coelomate segmentation: repeated muscular, nervous, excretory elements divided by septae annelida = little rings Fig. 33.22

19. ANNELIDA hydrostatic skeleton: fluid in coelom circulatory system: closed; Fig. S6-3 heart: muscular blood vessels dorsal, ventral blood vessel; Fig. S6-1 capillaries: small branches of blood vessels

20. ANNELIDA excretory system: metanephridia (Fig. 44.12) fluid enters nephrostome, passes through coiled tubule useful nutrients return to circ. system, wastes excreted via nephridiopore

21. ANNELIDA nervous system: ventral nerve cord with ganglia (swellings); brain muscular system: longitudinal and circular muscles locomotion: muscular contraction works against hydrostatic skeleton of coelom setae (bristles) digestive system: subdivided and more specialized hermaphroditic or dioecious

22. ANNELIDA leeches specialized as predators or blood feeders don’t confuse with trematode no obvious head; no septae or setae suckers for temporary attachment large digestive system for blood secrete hirudin: anticoagulant other secretions; osteoarthritis