1. Unsegmented Worms: Phylum Platyhelminthes & Phylum Nematoda
CH. 26-4

2. Phylum Platyhelminthes (Flatworms)

3. 3 Important Classes of Phylum Platyhelminthes :
TREMATODA – flukes
CESTODA – tapeworms
TURBELLARIA - small, free-living flatworms, sea slugs

4. Class Turbellaria (Planarians)
Soft, flattened bodies covered in cilia
Live in aquatic or marine environments
Carnivorous scavengers

5. Class Trematoda (Flukes)
Parasitic
Have a tough outer covering and two suckers to anchor to host and feed at the same time
Example: Schistosoma (liver fluke)

6. Class Cestoda (Tapeworms)
Parasitic
Live in the digestive tract of host

7. Identifying Characteristics of Phylum Platyhelminthes
Three true tissue layers (triploblast)
endoderm, mesoderm, ectoderm
Acoelomate (no coelom)
Bilateral symmetry
Cephalization
Some have eyespots (sensitive to light)
Motile (by undulation, cilia, or gliding over slime track)
Found in marine, freshwater and damp terrestrial habitats

8. Identifying Characteristics of Phylum Platyhelminthes
Gastrovascular Cavity (GVC)
In Planaria/Flukes: one opening in pharynx serves as both mouth and anus. Extracellular digestion
In tapeworms: intracellular digestion. No need for mouth since nutrients are pre-digested by host!
No circulatory or respiratory system
take in O2 through their body surface

9. Identifying Characteristics of Phylum Platyhelminthes
Excretory: flame cells (protonephridia) function like a kidney, remove water and chemical wastes through body pores
Nervous system:
Planarians/flukes: Simple brain, cephalization, ladder-like network of nerves
Tapeworms: extremely reduced nervous system
Reproduction:
Sexual: hermaphroditic (individuals capable of producing both eggs and sperm)
Asexual: by regeneration
May be free-living or parasitic

10. “Free-Living” Flatworms Planarians (Class Turbellaria)
Freshwater, free-living flatworm
Moves by beating cilia and gliding on a film of mucus
Common to most parts of the world
3-12mm in size
Have a head and simple brain!

11. Free-living Flatworms Planaria
Possess two eyespots (ocelli) that are sensitive to light.

12. Free-living Flatworms Planaria
Have a single opening to their GVC in the middle of their bodies called the pharynx
GVC branches into intestines
Planaria are carnivorous

13. Free-living Flatworms Planaria (handout)
Gastrovascular
Cavity

14. Planaria Reproduction
Sexual – Each planaria can both give and receive sperm
Usually mate with another worm. Self- fertilization is less common but possible
Mating with another worm is preferable (increases genetic diversity)
Eggs develop inside the planarian’s body
Asexual – by regeneration
Fragmentation
Spontaneous “dropping tails”

15. Planaria Regeneration
Planarians will spontaneously “fall to pieces” and each piece will grow a new worm!

16. Marine Flatworms

17. Marine Flatworm Penis Fencing

18. Penis Fencing Videos http://www.youtube.com/watch?v=wn3xluIRh1Y

19. Parasitic Flatworms: Tapeworm
No/extremely reduced nervous system
Parasite just attaches itself and absorbs food
No digestive tract
absorb nutrients that pass by
Covered in protective cuticle
Tough outer covering to
prevent being digested by host!

20. The Tapeworm: Up Close and Personal
Scolex or head (anterior end)
Four suckers and hooks to attach to the intestine of its host

21. The Tapeworm: Up Close and Personal
Proglottids: sections of tapeworm with reproductive structures.
Sexual reproduction: hermaphroditic (capable of producing both eggs and sperm)
Needs multiple hosts to complete its life cycle
Asexual reproduction: reproduce by segmentation.

22. New proglottids form from the head
Older, more mature proglottids are found further from the head

23. Tapeworm Video

24. Pork Tapeworm

26. Phylum Nematoda (Roundworms)
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27. Phylum Nematoda Commonly called roundworms
Range greatly in size (microscopic to meters long)
Many, many different species (perhaps more than a million
Most abundant animal on the planet numerically
C. elegans, a nematode, was first multicellular animal to have genome completely sequenced
May be parasitic or free-living
Free-living found in all climates
75% of species are parasitic and live within a host (hosts can be plants or animals)

28. Identifying Characteristics of Nematodes
Three true tissue layers (triploblastic)
endoderm, mesoderm, ectoderm
Pseudocoelom (cavity NOT fully lined by mesoderm like a true coelom)

29. Identifying Characteristics of Nematodes
Digestion:
Have a complete ONE WAY digestive tube with TWO openings! (separate mouth and anus)
Mouth, pharynx, long intestine, anus
Movement: longitudinal muscles only
Pseudocoelom acts as hydrostatic skeleton
Simple nervous system:
exhibit cephalization with nerve ganglia in head
ventral and dorsal nerve cords
Epidermis secretes a cuticle made of collagen to keep them from drying out

30. Identifying Characteristics of Nematodes
No respiratory or circulatory systems
Breathe and excrete wastes through body walls
Use diffusion to carry nutrients and wastes throughout body

31. Identifying Characteristics of Nematodes
Developed reproductive systems
Sexual reproduction: Sexes are separate in most species (some hermaphroditic). Fertilization inside female. Eggs develop either outside or inside nematode, depending on species
Phylum contains many parasitic and free-living forms found in fertile soil

32. Ecological Roles of Free-living Nematodes
Decomposers: they recycle bacteria, fungi and decaying, rotting organic matter back into the soil.
This means they are very important to the chain of energy production and matter recycling of the earth.

33. Negative Effects of Parasitic Nematodes
Invade many different types of crops and often cause crop death
Attack the bark of forest trees (pine wood nematode)
Invade the intestine of many mammals and cause sickness and often eventual death if untreated.
Soybean Cyst nematode: infects soybean plant crops and causes cysts on the plants

34. Parasitic Species of Nematodes include:
WHIPWORMS which invade the human large intestine. Are responsible for the disease “Trichinosis”
HOOKWORMS which invade the small intestine of dogs, cats and humans. They cause anemia as they suck blood voraciously
PINWORMS which invade the upper parts of the colon. Males are 1-4mm and females are 8-13 mm in length.
FILARIDS which invade many different parts of the body are responsible for a range of diseases (incl. elephantiasis and Loa Loa)
ASCARIDS which invade the human intestine and are responsible for the disease Ascariasis

35. Ascariasis Caused by Ascaris lumbricoides
Ascaris infection is prevalent in tropical regions with poor hygiene
Host becomes infected by ingestion of food contaminated with fecal matter containing eggs

36. Life lessons courtesy of the flatworms and nematodes:
#1: Don’t eat poop.
#2: Wash your hands!