Systematic Adaptations of Phylum Platyhelminthes

1. Systematic Adaptations of Phylum Platyhelminthes The Flatworms

2. Derived Characteristics • Organ level of organization • Well developed, specialized anatomical structures • Incomplete gastrulation • Gastrovascular cavity with one opening • Triploblastic • True mesodermal tissue filling space between endoderm and ectoderm (note “parenchyma”) • Bilateral Symmetry • 2 symmetrical sides about longitudinal axis • Cephalization • Concentration of sensory apparatus at anterior end

3. Body Form & Development • Acoelomate • Parenchyma derived from mesodermal tissue • Elongated body • No appendages

4. Integumentary • Simple integument • Ciliated in free living flatworms, but lacking cilia in parasitic forms • Glandular tissue associated with skin • Mucous glands • “Dual gland” for adhesion and release

5. Skeletal & Muscular • Hydrostatic Skeleton • Parenchymal tissue holds a constant (“static”) volume of water (“hydro”) • Compression/contraction in one direction must necessarily result in expansion/elongation in a different direction • Well developed muscles are present in the body wall • Longitudinal • Circular • Oblique

6. Muscular arrangement • Predict the result from the contraction of: • Longitudinal muscle (2) • Circular muscle (1) • Oblique muscle (3)

7. Watch these flatworms move • https://www.youtube.com/watch?v=zCH37KI_R_E • https://www.youtube.com/watch?v=HekwSO6dBG0 • https://www.youtube.com/watch?v=OCOYrHAkjVE

8. Nervous & Sensory • Centralized nervous system • Paired solid, ventral nerve cords • “Ladder” type nervouse organization – Transverse nerves connecting longitudinal nerve cords • Concentration of nerve tissue forming cephalic ganglia (simple brain)

9. Nervous & Sensory • Cephalization • Concentration of sense organs in anterior body region • Sense organs • Photoreceptors (note “ocelli”) • Chemoreceptors (note “auricles”)

10. Digestion • The development of the digestive cavity is incomplete, forming a gastrovascular cavity with a single opening • Digestion is largely extracellular, although some flatworms complete the process in food vacuoles (intracellular) • The class turbellaria are free living and carnivorous, and have well developed gastrovascular cavities • The other classes of flatworms are parasitic, dependent upon the host for digestion

11. Digestion • Mouth located ventrally • Free living turbellaria have an extensible pharynx • The highly branched gastrovascular cavity brings digested food in close proximity to all body tissues • As the gastrovascular cavity has only 1 opening, wastes are excreted through the pharynx or retained

12. Watch these flatworms feeding • https://www.youtube.com/watch?v=9QJF93WlNew • https://www.youtube.com/watch?v=eUmOJ6fWN9w&feature=endscreen&NR=1 • https://www.youtube.com/watch?v=Ich4Y_K6GuM

13. Digestion • The gastrovascular cavity in parasitic forms is diminished (as in this photo) or absent (as in the tapeworms) • When present, the gastrovascular cavity is generally Y shaped

14. Osmoregulation vs. Excretion? • Osmoregulation is the removal of excess water • Excretion is the removal of metabolic waste (mostly nitrogen compounds like ammonia or urea that accumulate from metabolism of protein) and excess dissolved materials (salts) • The flame cells are concerned with osmoregulation • Metabolic wastes are generally removed by simple diffusion

15. Excretion & Osmoregulation • “Protonephridia” – primitive excretory tubules driven by Flame Cells. • The “flame” consists of several flagellae that drive fluids through tubules that lead to collecting tubules

16. Excretion & Osmoregulation • There is considerable variation in the structure of osmoregulation systems in the flatworm classes, from simple excretory pores to a bladder

17. Reproduction • Due to the simplicity of the flatworm body form, many are capable of reproducing asexually. In low density populations, asexual reproduction (by budding or fission) may be predominant • Flatworms are monoecious (one reproductive form – AKA hermaphroditic) but generally are unable to self-fertilize • Parasitic forms have complex life cycles, often involving one or more intermediate hosts.

18. Flatworm reproductive organs • This flatworm is free living. Its muscular and digestive systems, while not shown above, are well developed • Note the presence of both male and female gonads (Monoecious)

19. Fluke reproductive organs • This liver fluke is parasitic. It depend on its host for locomotion and digestion, allowing it to devote more of its energy and anatomy to reproduction • Note that is also is monoecious. The testes are more pink, and located posteriorly • The ovary is darker and more centrally located

20. Tapeworm reproductive organs • Tapeworms are parasitic. Their digestive system is absent. Almost their entire anatomy is devoted to reproduction • They have a segmented body, with both testes and ovaries located in each segment

21. Life cycle of the Liver fluke

22. Trematode Life Cycle • https://www.youtube.com/watch?v=r7okJ6wHYLA • https://www.youtube.com/watch?v=EEBbtwGqPEs • https://www.youtube.com/watch?v=9fmx24FbZoM

23. Classes of Platyhelminthes • The Phylum platyhelminthes is divided into 4 classes • Class Turbellaria – The free living flatworms • Class Trematoda – The digenetic flukes • Digenetic = 2 or more hosts • Class Monogenea – The monogenetic flukes • Monogenetic = 1 host • Class Cestoda – The tapeworms

24. Class Turbellaria • The only class of free living flatworms • Ciliated epidermis with mucous secreting rhabdites • Acoelomate • Extensible pharynx • Includes the planaria

25. Class Trematoda • Parasitic flukes • Syncytial tegument (multinucleate skin) without cilia • Y shaped gastrovascular cavity • Oral sucker for obtaining food and ventral sucker for attachment • No hooks for attachment to host • Digenetic – 2 or more hosts • Intermediate host – usually an invertebrate, frequently a mollusc • Definitive host – a vertebrate • Includes fasciola, schistosoma and clonorchis

26. Class Monogenea • Parasitic flukes • Syncytial tegument (multinucleate skin) without cilia • Free living, ciliated larvae • Y shaped gastrovascular cavity • A single oral sucker • A series of posterior hooks (opisthaptor) for attachment to the host • Monogenetic – parasitic on a single host, usually a fish, amphibian or reptile

27. Class Cestoda • Tapeworms, parasitic to the digestive tracts of vertebrates • Syncytial tegument without cilia • The tegument is covered with fingerlike extensions to increase the surface area for food absorption • Gastrovascular cavity is absent • Anterior structure (scolex) with hooks/suckers for attachment to the host • Body is formed into segments called proglottids. Each proglottid has testes and ovaries. Self-fertilization is possible • Gravid proglottids from feces of infected animals may be consumed by a new host, or may be spread by consuming larvae in the flesh of an infected animal

28. Tapeworms • https://www.youtube.com/watch?v=Q5BuXmDIJxs • https://www.youtube.com/watch?v=9qyEfeg-334