1. Unit 4 - Phylums Platyhelminthes and Nematoda
Flatworms and Roundworms

2. Phylum Platyhelminthes
Largest group of acoelomate (no body cavity) worms
Flatworms with middle tissue layer- mesoderm
Tissues organized into organs
Bilaterally symmetrical and flat
Cells lie close to exterior enabling efficient diffusion of oxygen and carbon dioxide
Highly branched gastrovascular cavity runs close to all tissues giving cells ready access to food
No respiratory or circulatory systems

3. Coelom – Body Cavity
The coelom usually performs multiple functions, including one or more of the following:
Provides room for organ development
Surfaces for diffusion of gases, nutrients, and wastes
Storage
Hydrostatic support

4. Phylum Platyhelmithes
Flatworms
Liver Flukes, Planaria and tapeworms
Marine flatworms
Characteristics:
Ribbon-like bodies
Bilateral symmetry
Branched digestive system
No skeleton
Asexual (fission); Hermaphrodites (sexual)
Free movement
Skin breathing

5. Phylum Platyhelminthes
Class Turbellaria
Most free-living; marine
Dugesia- Freshwater planarians
Digestion- Nutrients absorbed by intestinal wall and waste goes out through mouth
Muscular pharynx comes out of central mouth to feed

6. Phylum Platyhelminthes
Reproduction- Mostly asexual by attaching posterior end to stationary object and pulling into two
Hermaphrodites can reproduce sexually
Nervous system: Brain, two nerve cords, and light-sensitive eye spots
Water balance- Water continually enters by osmosis
Flame cells with cilia draw water to the outside

7. Phylum Platyhelminthes
Marine flatworm

8. Phylum Platyhelminthes

9. Planarian

10. Phylum Platyhelminthes
Many parasitic
Endoparasite- internal
Ectoparasite- external
Class Cestoidea
Subclass Eucestoda- Parasitic flatworms (tapeworms)
Suckers and hooks on scolex (head) attach to walls of intestines and food absorbed from host’s intestines directly through the tapeworm’s skin

11. Phylum Platyhelminthes
String of rectangular body sections (proglottids)
Each proglottid is a reproductive unit
Added continually through life
May grow up to 12 m (40 ft.) long

12. Phylum Platyhelminthes
Most occur in vertebrates
Dozen types in humans
Taenia saginata- Beef tapeworm
Live in cow muscles in cysts
High temp. kills larvae
Subclass Cestodaria
Body not subdidvided into proglottids
Larvae in crustaceans; adults in fish

13. Scolex Examples

14. Phylum Platyhelmithes

15. Proglottid – reproductive structure

16. Phylum Platyhelminthes
Largest flatworm class, Trematoda
Parasitic worms called flukes
Endoparasites or ectoparasites
Subclass Aspidogastrea (Aspidobothrea)- Endoparasite of mollusks
Subclass Digenea- Endoparasites of vertebrates

17. Phylum Platyhelminthes
Tegument- thick protective covering prevents them from being digested
Take nourishment directly from hosts
Use suckers to attach and the muscular pharynx to suck nourishment from host’s body fluids

18. Phylum Platyhelminthes
Complex life cycles involve more than one host
Ex: Schistosoma- Responsible for schistosomiasis
From contaminated water
Larvae bore into host skin into blood vessels of intestines
Block vessels causing bleeding and damage to liver
Snail is intermediate host

19. Phylum Platyhelminthes
Class Monogenea –
Monogenetic flukes
One life cycle in one host
Mostly ectoparasites on vertebrates

20. Phylum Platyhelminthes
Liver fluke

21. Phylum Nematoda
Roundworms- have a pseudocoelom (body cavity between endoderm & mesoderm)
Fluid movement serves as circulatory and gas exchange system
Fluid also distributes nutrients to cells from digestive system

22. Phylum Nematoda Long, cylindrical bodies
Majority microscopic and free-living
One-way digestive system
Thick, flexible epidermis protects and gives shape
Layer of muscle underneath pulls at epidermis and pseudocoelem for whip-like movement

23. Phylum Nematoda Roundworms Ascaris, Trichinella and hookworms
Characteristics:
Flattened bodies
Bilateral symmetry
Many are parasites
Fluid-filled body cavity called a pseudocoelem
Digestive tube
No skeleton
Sexual reproduction (Internal fertilization)
Sperm is amoeboid
Free movement
Skin breathing

24. Phylum Nematoda
Class Secernentea (Phasmidea)- Phasmids (sensory structures) in tail
Ascaris, Enterobius, Rhabditis, Turbutrix, Necator, and Wuchereria
Class Adenophorea (Aphasmidia)- No phasmids
Dioctophyme, Trichinella, Trichuris
50 species are parasitic
Plant parasites feed on living plant cells in all parts of plant, causing wilting and withering
14 species affect humans
Ex: Enterobius (pinworms), Ascaris lumbricoides, Trichinella spiralis, Necator (hookworms)

25. Phylum Nematoda
Trichinella infects pigs and causes trichinosis (serious disease caused by eating undercooked pork)
Necator live in warm, moist soils of the tropics
Hookworm larvae enter bloodstream through soles of feet

26. Phylum Nematoda Ascaris Carried in human waste
After ingestion, eggs hatch into larvae in intestines
Larvae bore through blood vessels, enter blood stream and then lungs (causes respiratory distress)
Larvae may enter gallbladder or pancreas causing blockages
Return to intestines to mature and mate
May grow up to 1 ft. in length

27. Phylum Nematoda
Ascaris
Trichinella

28. Trichinosis Trichinella spiralis is found in pork
Trichinosis is a disease caused by the Trichinella worm.
Eggs hatch in the host’s gut
Symptoms:
Diarrhea
Fever
Muscle pain
Death

29. Common Parasitic Roundworms
Hookworms attach to the inside of the digestive tract
Often found in pets
Pinworms- most common
Heartworms- transmitted to dogs by mosquitos
Filarial worms- live in blood where they block blood vessels or lymph vessels causing severe swelling (Elephantitis)
Guinea worm- Ingested with contaminated water
Cause dracunculiasis
Only found when exiting skin
Found in Africa, India and Pakistan