1. ZOO 115 Invertebrate Zoology
Platyhelminthes
Parasites

2. Parasitism - Adaptations
Method of attachment
SUCKERS - Trematoda and Monogea
SUCKERS AND HOOKS - Cestoidea
home.earthlink.net/~xylaria/em/tapeworm.jpg

3. Parasitism - Adaptations
Getting into host
Penetration – special glands to digest skin
a.abcnews.com/images/2020/pd_eating_070521_ms.jpg
static.howstuffworks.com/gif/mosquito6a.jpg
Getting into host
Passive – eaten by host
Need outer resistant covering
Living tegument
Permeable to H20, amino acids, sugars
Tolerate great changes in pH.

4. Parasitism - Adaptations
Osmotic Pressure
Must be lower than surroundings – why?
Facultative anaerobic respiration
4X more efficient than in vertebrates
Reduced structures
Sensory (except chemo)
Muscles
Nervous system
Digestive tract

5. Parasitism - Adaptations
Increased reproduction
Produce many many eggs
e.g. Fish tapeworm 2 million eggs/day and can live for 15 yrs (100 trillion eggs in lifetime)
Polyembryony – many young from one egg.
Asexual stages amplify numbers
e.g. Fasciola hepatica produces 500,000 eggs in a lifetime that produce 42 trillion offspring.

6. Parasitism - Adaptations
Host reactions to parasites
Susceptibility varies with life cycle and health of host
Single host – parasite usually becomes more commensal
Castration
Multiple hosts – parasite can kill the host
Snails
Ants
Internal parasites – develop ways of hiding from immune system

7. Parasitism - Adaptations
Host specificity varies
Some are completely specific to their hosts
Problems with non-specificity
Swimmer’s itch
Nematode and encephalitis

8. Class - Trematoda Common Name - Flukes
Common parasites of all major vertebrate taxa.
>11,000 species

9. Class Trematoda - General Anatomy of Adult
Suckers for feeding and attachment
web.bio.utk.edu/guffey/BiaB
Non-cliated tegument
Protection against enyzmes,
Gas exchange
Eliminate nitrogenous waste
Absorb glucose and amino acids

10. Class Trematoda - General Anatomy of Adult

11. Class Trematoda – Life Cycles
Chinese Liver Fluke (Opisthorchis or Clonorchis)
Infests 20 million E. Asians
Adult ~ 2.5 cm in length
Live 8 yrs
Produce 4000 eggs per day for 6 mo
Symptoms: Jaundice, gallstones, debilitation and liver cancer

12. Class Trematoda - Life Cycle
Metacercaria
biodidac.bio.uottawa.ca/ftp/BIODIDAC/Zoo/Platyhel/DIAGBW
Sporocyst
Amplification
ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/slides
Cercaria
Redia
bio.winona.msus.edu/bates/Parasitology/Images/
Miracidium /
Adult
ucdnema.ucdavis.edu/imagemap/nemmap/ent156html/slides
Cercaria

13. Class Trematoda – Life Cycles
Blood Fluke (Schistosoma sp)
Dioecious: Male 6-10 mm, Female much smaller (fits into groove in male)
Develop cercaria directly from sporocyst (no redia) /
Male
Female

14. Class Trematoda - Reproduction
Why is amplification important?
What impact might the multiple host strategy of the parasite have on the hosts?

15. Class Monogenea Ectoparasites – only one host
Ectoparasites – only one host
Mostly infest fishes
bioweb.uwlax.edu/zoolab/Table_of_Contents/Lab-4a/Class_Monogenea
Adults have suckers and hooks
Larvae – hooked free-swimming (oncomiradium)

16. Class Monogenea – life cycles
Dactylogyrus sp.
More eggs with increasing temperature
Eggs released – sit on bottom
Hatch into swimming larvae
On contact with fish metamorphose into adult form

17. Class Monogenea – life cycles
Polystoma sp.
Eggs stay in frog until frog gets in water
Hatch into swimming larvae
Larvae attach to gills of tadpoles
Tadpoles metamorphose and larvae crawls over belly and goes into bladder

18. Class Cestoda Common name: Tapeworms ~3400 species
faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files
Common name: Tapeworms
~3400 species
Gut is absent – specialized neodermis for nutrient uptake.
Live about yrs
Can copulate

19. Class Cestoda - Anatomy
Neck
Suckers
Hooks
Scolex
Can reach 15 m in length!
news.bbc.co.uk/media/images/
Head region
Attach to prey’s intestinal tract

20. Class Cestoda - Anatomy
Proglottids
Each is a complete hermaphroditic reproductive system
Both Cross and Self-Fertilization
biodidac.bio.uottawa.ca/ftp/BIODIDAC/ZOO/PLATYHEL/PHOTO/

21. Class Cestoda – Life Cycles
biodidac.bio.uottawa.ca/ftp/BIODIDAC/ZOO/PLATYHEL/PHOTO/
bioweb.uwlax.edu/zoolab/Table_of_Contents/Lab-4b/

22. Class Cestoda – Life Cycles
If eggs go in water
swimming larvae (onchosphere) hatches within 10 days
Eaten by copepods
Copepods eaten by fish
Penetrates gut, migrates to muscle and transformed into dormant miniaturized adult
Eaten by warm-blooded host
users.rcn.com/jkimball.ma.ultranet/BiologyPages/

23. Class Cestoda – Life Cycles
If eggs go on land
Eggs eaten by cattle
Onchosphere larvae hatch, bore into intestinal wall and transported through circulatory system to muscle tissue
Develops into bladderworm larvae (Cysticercus).
Eaten by warm-blooded host.

24. Class Cestoda Causes Diarrhea, Weight loss and inflammation
Biggest problem is accidental infestations
Bladder worm will develop into tissue other than muscle.
Cyst can contain liters of fluid which could cause severe infection if released