The document summarizes two phyla - Acoelomorpha and Platyhelminthes. Acoelomorpha includes about 350 small, bilaterally symmetrical flatworm species typically found in marine sediments. They lack major organ systems and rely on diffusion. Platyhelminthes includes an estimated 20,000-30,000 species of flatworms including the parasitic groups Trematoda, Monogena and Cestoda as well as the free-living Turbellaria. They are acoelomate and range from predators to parasites with complex life cycles utilizing multiple hosts. Major characteristics include an epidermis/tegument, muscles, digestive systems ranging from extensible pharyng

1. Acoelomorpha and
Platyhelminthes

4. Acoelomorpha
Diversity
- 350 species
- 2 clases: Acoela and Nemertodermatida

5. Acoelomorpha

6. Acoelomorpha
Where found?
- Typically in marine sediments
- Some are pelagic (inhabit open ocean)
- Some live in brackish water

7. Acoelomorpha
General characteristics
- Bilaterally symmetrical
- Acoelomate
- Between epidermis and digestive cavity
is mesodermally derived parenchyma
- Not protostomes
Ectoderm
Mesoderm
Endoderm
Gut cavity

8. Phylum Acoelomorpha
Body plan
- Small (<5mm), flat worms
- Bilaterally symmetrical
- Dorsoventrally flattened
- Ciliated epidermis for movement
- Digestive system absent or blind
- Simple pharynx may be present

9. Phylum Acoelomorpha
Homeostatic structures and functions
- No respiratory system
- No circulatory system
- No osmoregulation
- No excretion
- All achieved by diffusion
- Nervous system
- Sense organs include statocysts and ocelli
- Diffuse system of anterior neurons
- Not quite a ganglion

10. Phylum Acoelomorpha
Reproduction
- Monoecious
- Eggs are produced
- Cleavage is spiral (duet-spiral)

11. Protostomia
Division into Protostomia or Deuterostomia is largely based on development
- Fate of the balstopore
Within the Protostomia are two large clades
- Lophotrochozoa and Ecdysozoa
- Members of the Lophotrochozoa share either a horseshoe-shaped feeding structure
(lophophore) or a larval stage known as the trochophore.

13. Phylum Platyhelminthes
Diversity
- 20,000 - 30,000 species?
- Turbellaria
- Trematoda
- Monogena
- Cestoda

15. Platyhelminthes

16. Platyhelminthes
Where found?
- Turbellarians are mostly free-living
- Inhabit fresh and marine waters; terrestrial in moist climates
- Trematodes, Monogens, and Cestodes are all parasitic
- Inhabit different regions of the body
- Many inhabit different hosts during development

17. Platyhelminthes
General characters
- Difficult to generalize across the phylum
- Acoelomate (triploblastic)
- Protostomes
- Bilateral symmetry
- Dorsoventrally flattened

18. Platyhelminthes
General characters
Epidermis and muscles
- Turbellarians have a cellular,
ciliated epidermis
- Contains rhabdites - produce protective
mucus when disturbed
- Dual-gland adhesive organs - three
cells: viscid, releasing, and anchor

19. Platyhelminthes
General characters
Epidermis and muscles
- Turbellarians have a cellular,
ciliated epidermis
- Contains rhabdites - produce protective
mucus when disturbed
- Dual-gland adhesive organs - three
cells: viscid, releasing, and anchor

20. Platyhelminthes
General characters
Epidermis and muscles
- Trematodes, Monogenes, and
Cestodes all have syncytial
tegument
- Many nuclei enclosed within single cell
membrane
- Thought to aid against host defenses

21. Platyhelminthes
General characters
Epidermis and muscles
- Muscles are found just inside of
epidermis or tegument
- Circular, longitudinally, and diagonally
- Parenchyma fills space between
muscles

22. Platyhelminthes
General characters
Nutrition and Digestion
- Generally, platyhelminths have a mouth, pharynx, and intestine
- Turbellarians have a pharynx capable of being extended from the body
- Most are predaceous and ensnare prey in mucus before consuming
- Utilize both intracellular and extracellular digestion
- Gut is blind; undigested food exits through mouth

23. Platyhelminthes
General characters
Nutrition and Digestion
- Monogenes and trematodes also possess a mouth, but pharynx not
extensible
- Graze on host cells, cellular debris, and body fluids
- Blind gut

24. Platyhelminthes
General characters
Nutrition and Digestion
- Cestodes have no digestive system
- Absorb nutrients from their host via diffusion

25. Platyhelminthes
General characters
Excretion and Osmoregulation
- Excretion for wastes; osmoregulation for water balance
- Turbellarians, trematodes, and monogenes utilize protonephridia (flame cells)
- Mostly osmoregulatory
- Reduced or absent in marine forms that do not have to cope with excess water
- Cestodes have excretory canals that run the length of the body

26. Platyhelminthes
General characters
Excretion and Osmoregulation

27. Platyhelminthes
General characters
Excretion and Osmoregulation

28. Platyhelminthes
General Characteristics
Nervous System
- Some turbellarians have a nervous system analogous to a nerve net.
- More advanced nervous systems consist of longitudinal nerve cords
- Brain is bilobed mass of ganglion cells
- Some specialization among neurons: sensory, motor, and association

29. Platyhelminthes
General Characteristics
Sense organs
- Ocelli are present in all but cestodes
- Tactile cells and chemoreceptors are abundant.
- Statocysts are present in some.

30. Platyhelminthes
General Characteristics
Reproduction
- All are monoecious; most practice cross-fertilization
- Turbellarians
- Both asexual (fragmentation) and sexual
- Trematodes
- Utilize multiple hosts with several life stages
- Monogenes
- Single host
- Cestodes
- Utilize multiple hosts

32. Platyhelminthes
Class Turbellaria
- Mostly free-living
- Marine, fresh, and terrestrial
environments
- Extreme powers of regeneration

33. Platyhelminthes
Class Turbellaria

34. Platyhelminthes
Class Trematoda
- All parasitic flukes; almost all parasitize vertebrates
- Leaf-like with one or more suckers for attachment
- Structures aiding parasitic lifestyle
- Penetration and cyst glands
- Organs for adhesion (suckers and hooks)
- Increased reproductive capacity

35. Platyhelminthes
Class Trematoda
- Clonorchis spp.
- Most important liver fluke
- Important in SE Asia

36. Platyhelminthes
Class Trematoda
- Clonorchis spp.
- Life cycle
- Adults reside in bill passageways of
humans
- Eggs shed into water with feces
- Eggs hatch after they are ingested by a
snail
- In snail, miracidium -> sporocysts ->
redia -> cercaria (lots, 250,000!)
- Cercaria escape into water and burrow
into fish muscle
- If not cooked before eaten, human
infected

37. Platyhelminthes
Class Trematoda
- Schistosoma spp.: blood fluke
- Africa, SE Asia, S. America, Middle
East, West Indies
- Dioecious
- Males larger than females and with
gynecophoric canal
- Groove into which the female fits

38. Platyhelminthes
Class Trematoda
- Schistosoma spp.: blood fluke
- Life cycle
- Eggs shed with feces or urine
- Hatch in water as miracidia
- Must find snail
- In snail transform into sporocysts
- Sporocysts give rise to cercariae
- Cercariae escape snail and bore into
human skin

39. Platyhelminthes
Class Monogenea
- All parasitic, but mostly
ectoparasitic
- Parasitize gills and external
surfaces of fish
- Appear not to cause much damage
to host
- True outside of very high fish densities;
not true with high densities
- Attachment by opisthaptor

40. Platyhelminthes
Class Cestoda
- Long, flat bodies
- Scolex for attachment
- Linear series of reproductive units (proglottids)
- Digestive system lacking
- Surface covered with projections similar to microvilli (increases surface area)
- Require at least two hosts

41. Platyhelminthes
Class Cestoda
- Taenia spp. life cycle
- eggs/proglottids shed in feces
- Ingested by cattle/pig
- Oncospheres develop in muscle tissue
- If raw or undercooked beef/pork
ingested, human infected

42. Platyhelminthes
Class Cestoda
- Dipylidium caninum life cycle
- Fleas play an important role