1. Ch 10 Acoelomate Bilateral Animals

2. Acoelomate Bilateral Animals Consist of phyla: –Phylum Platyhelminthes –Phylum Nemertea –And others

3. Acoelomate Bilateral Animals Reproductive and osmoregulatory systems 1.Simplest organisms to have bilateral symmetry 2.Triploblastic 3.Lack a coelom 4.Organ-system level of organization 5.Cephalization 6.Elongated, without appendages

4. Bilateral Symmetry Divided along sagittal plane into two mirror images –sagittal= divides bilateral organisms into right and left halves

5. Anterior= head end Posterior= tail end Dorsal= back side Ventral= belly side

6. Bilateral animals Bilateral symmetry = important evolutionary advancement –Important for active, directed movement Anterior, posterior ends –One side of body kept up (dorsal) vs. down (ventral)

7. Directed movement evolved with anterior sense organs  cephalization Cephalization –specialization of sense organs in head end of animals

8. Acoelomates lack a true body cavity –Solid body –no cavity b/w the digestive tract and outer body wall

10. Acoelomates are triploblastic Triploblastic (3 germ layers) –Germ layer= layers in embryo that form the various tissues and organs of an animal body

11. 3 germ layers Ectoderm –Outermost germ layer –Gives rise to outer covering of animal ie. epidermis Endoderm –Innermost germ layer –Gives rise to inner lining of gut tract

12. Mesoderm –Middle germ layer –b/w ectoderm and endoderm –Gives rise to various tissues/organs (ie. muscles)

13. Acoelomate animals have an organ-system level of organization

14. Digestive tract and nervous system Organ-system –Different organs operate together (ie. excretory system, nervous system) –mesodermal tissue gives rise to parenchyma

15. Polyclad http://www.rzuser.uni-heidelberg.de/~bu6/ From Red Sea

16. Phylum Platyhelminthes Flatworms Free living Parasitic

17. From Atlantic ocean http://www.rzuser.uni-heidelberg.de/~bu6/

18. Phylum Platyhelminthes Flattened dorsoventrally –flatworms 34,000 species Gastrovascular cavity (if present) has only one opening (mouth = anus) Mostly monoecious

19. Phylum Platyhelminthes First phylum that has an Organ systems present –derived mesodermally (parenchyma): Muscular system Digestive system (incomplete; gastrovascular type) (absent in some) Nervous system Excretory system (absent in some) Reproductive system

20. Phylum Platyhelminthes Organ systems absent: –Circulatory –Respiratory Rely on diffusion

21. Phylum Platyhelminthes (cont’d) Hymenolepsis- rat tapeworm Divided into 4 classes: –Class Turbellaria (mostly free-living flatworms) –Class Cestoda (tapeworms) –Class Trematoda (parasitic flukes) –Class Monogenea (parasitic flukes)

22. Class Turbellaria Mostly free-living flatworms Marine (mostly) or freshwater bottom- dwellers Predators and scavangers First group of bilateral symmetrical animals

23. Class Turbellaria (cont’d) Move by muscles, ciliated epidermis

24. Class Turbellaria (cont’d) Freshwater turbellarians adapted osmoregulatory structures –Protonephridia protos= first nephros= kidney network of fine tubules running down sides of organism

25. Class Turbellaria (cont’d) –Flame cells= branch from tubules Ciliary projections drive fluid down tubule –Tubules open to outside= nephridiopore

26. Class Turbellaria (cont’d) nervous system with nerve ganglion –ganglion- aggregation of nervous tissue Cephalization- cerebral ganglion= primitive brain

27. Class Turbellaria (cont’d) Ocelli= light-sensitive eyespots

28. Turbellarian Reproduction Reproductive and osmoregulatory systems Asexual (fission) –transverse Sexual –Monoecious (mostly) –Cross-fertilization

29. Other 3 classes: –Class Trematoda –Class Cestoda –Class Monogenea All parasitic lack cilia Have unusual body covering: tegument Outer zone of tegument (glycocalyx) consists of proteins and carbohydrates aids in transport of nutrients, waste, gases Protection against host defenses

30. Class Trematoda Parasitic flukes Endoparasites –Hooks, suckers, increased reproductive capacity

31. 1mm-6cm long Complex life cycle: 1.Definitive host (primary/final host) – where parasite matures and reproduces (sexually) (eggs released) –vertebrate

32. 2.Intermediate host –Mollusc (ie. snail) –Hosts in which larval stages develop and undergo asexual reproduction – Results in an increase in the number of the individuals

33. Class Trematoda –Example: Chinese Liver Fluke

34. Chinese Liver Fluke Infects 30 million people in eastern Asia Lives in ducts of liver –Eats epithelial tissue, blood Definitive host: –Humans, dogs, cats 2 intermediate hosts: –snail –fish

35. Class Cestoda Tapeworms Endoparasites Vertebrate host –Live in digestive tract 1 mm- 25m long (EWWWW!!) Hymenolepsis- rat tapeworm

36. Class Cestoda Highly specialized Lack mouth, digestive tract –Absorb nutrients across body wall Hooks and suckers –“head”= scolex Hymenolepsis- rat tapeworm

37. Adult tapeworms consist of long series of repeating units= proglottids Chain of proglottids= strobila

38. Tapeworms are monoecious (mostly) –Mostly cross-fertilization No specialized sense organs scolex

39. Cestodes depend on host digestion –Small molecules in host intestine, liver

40. Definitive host= human Intermediate host= cattle Beef Tapeworm

41. Class Monogenea Parasitic flukes Mostly ectoparasites Single host, mostly fish

42. Phylum Nemertea Triplobastic, acoelamate bilateral symmetry Unsegmented Ciliated epidermis Closed circulatory usually <20cm Marine mud, sand Elongate, flattened worms

43. Phylum Nemertea (cont’d) Unlike the platyhelminthes, Complete digestive tract, with anus –One-way –More efficient; allows larger growth

44. Phylum Nemertea (cont’d) Cerebral ganglion, longitudinal nerve cords Long proboscis used in carnivorous species Two lateral blood vessels yet no heart Dioecious –“two” “house” –Male and female organs in separate individuals