1. Phylum Platyhelminythes

2. Platyhelminthes ~ 20,000 extant species Parasitic + free-living
Unsegmented flatworms

3. Platyhelminthes Triploblastic, acoelomate, bilaterally symmetrical
Incomplete gut; absent in some parasitic forms
Cephalization of nervous system
Protonephridia: excretion and osmoregulation
Hermaphroditic

4. Support
Hydrostatic skeleton
Elastic body wall
Body musculature

5. Taxonomy Class Turbellaria Class Monogenea Class Trematoda
Class Cestoda

6. Class Turbellaria Free-living flatworms Most are aquatic
Epidermis cellular and ciliated

7. Feeding and digestion in Turbellaria
Consume invertebrates (few herbivores and omnivores)
Locate food via chemoreception
A few are symbiotic

8. Turbellaria digestive system
Mouth, pharynx, intestine = incomplete gut
Pharyngeal glands produce mucus and proteolytic enzymes
Digestion extracellular, then phagocytization in intestine

9. Turbellaria nervous system
Sense organs
Tactile receptors cover body - concentrated anteriorly
Chemoreception = location of food
Statocysts = gravity detection and orientation
Photoreceptors
Inverted pigment cup ocelli
Negative phototaxis

10. Turbellaria nervous system
Variable: simple net-like to cephalized & bilateral
Ladder-like NS = more recently evolved

11. Class Monogenea Monogenetic flukes (life cycle = one host)
Body covered by tegument
Oral sucker reduced or absent
Ectoparasitic (usually fish)

12. Class Monogenea Monogenetic flukes (life cycle = one host)
Eggs hatch into ciliated larvae = oncomiracidia
Mature and find host

13. Class Trematoda Digenetic flukes (multiple hosts) Body with tegument
One or more suckers present
Internal parasite

14. Fluke Digestive System
Feed on host tissues and fluids (muscular pharynx)
Or, material in host gut
One-way digestive tract: mouth, muscular pharynx, short esophagus, intestinal cecae

15. Fluke Nervous System Ladder-like Cerebral ganglion
Suckers with tactile receptors (bristles and spines)

16. Sexual repro flukes Hermaphroditic Mutual cross fertilization
Male structures
Variable testes
Monogenetic = many
Digenetic = two
Sperm-to sperm duct, copulatory apparatus, eversible cirrus

17. Sexual repro flukes Female Structures Ovary to oviduct to ootype
Oviduct joined by vitelline duct
Seminal receptacle = blind pouch off of oviduct
Single uterus sometimes modified as vagina near female gonopore

18. Fluke reproduction Mutual cross-fertilization
Sperm stored in seminal receptacle
Eggs - oviduct to ootype then fertilized
r-selected strategy (high fecundity)

19. a – acetabulum
d - vitelline ducts
f - vitelline follicles
o - oral sucker
oe – oesophagus
oo – ootype
ov – ovary
ph – pharynx
sr - seminal receptable
t – testis
u - uterus

20. Fluke life-cycles Monogenetic Digenetic One host
Mostly external parasites of fish
Digenetic
Two or more hosts
Mostly internal parasites

21. Fluke life-cycles: Chinese liver fluke

22. Fluke life-cycles Digenetic Fasciola = sheep liver fluke
Multiple hosts
Internal parasite of vertebrates
Intermediate host usually gastropod

23. Fluke life-cycles Schistosoma mansoni
Schistosomiasis = disease with problems from egg production, fevers, eggs lodged in various tissues

24. Schistosomiasis

25. Schistosoma spp. cause swimmer’s itch

26. Class Cestoda Tapeworms Internal parasite Body with tegument
Body with anterior scolex, short neck and proglottids
No digestive system

27. Tapeworms = cestodes Locomotion Attachment
Sedentary: adult on host intestinal wall
Capable of muscular undulations
Attachment
Scolex
Anterior with hooks or adhesive pad

28. Tapeworm digestion No mouth, no digestive tract
Nutrients absorbed across tegument

29. Tapeworm Nervous System
Cerebral ganglion; nerve ring in scolex
Each proglottid has additional ganglia; connect to longitudinal nerve cords
Sensory organs reduced, tactile receptors in scolex

30. Sexual Repro: tapeworms
Hermaphroditic
Mutual cross-fertilization
Self-fertilization in some

31. Proglottids Numerous testes along margins
Collecting tubules to coiled sperm duct
Vas deferens to genital pore

32. Proglottids
Two ovaries
Uterus = blind sac

33. Tapeworm sex and fertilization
Cirrus of each mate inserted into genital pores
Sperm stored, eggs fertilized in oviduct
Capsule material and yolk cells stored in uterus
When mature, proglottids break free

34. Beef Tapeworm Life Cycle

35. Pork Tapeworm Life Cycle