1. Platyhelminthes
Flatworms

2. Characteristics Three germ layers Bilateral symmetry
Triploblasitc
Bilateral symmetry
Definite polarity of anterior & posterior ends
Body flattened dorsoventrally
Oral & genital apertures on mostly on ventral side

3. Characteristics Epidermis may be cellular or syncytial (ciliated)
Acoelomate (no internal body space)
Other than digestive tube
Incomplete digestive system (absent in some)
Nervous system
Pair of anterior ganglia with
longitudinal nerve cords

4. Characteristics Nutrition & Digestion Tapeworms lack digestive system
Digestive system includes a mouth, pharynx, & intestine
Intestines may be simple or branched
Extracellular digestion
Intestinal secretions contain proteolytic enzymes
Food sucked into intestines where cells will complete digestion
(intracellular)
Undigested food is egested through pharynx
Tapeworms lack digestive system
Absorb nutrients (predigested by host) directly through tegument.

5. Characteristics Simple sense organs; eyespots in some Excretory system
Two lateral canals with branches bearing flame cells
Flame cell’s function on the basis of filtration & reabsorption.
Lacks respiratory, circulatory, & skeletal systems
Most are monoecious

7. Characteristics Reproduction Asexual Sexual Both asexual & sexual
Fission
(constricts behind pharynx & separates into 2, each regenerates the missing parts)
Budding
Some tapeworms can bud off thousands of juveniles
Sexual
Although monoecious (hermaphroditic) most practice cross- fertilization.

9. Phylum Platyhelminthes
Four classes
Turbellaria
Monogenea
Trematoda
Cestoda

10. Class Turbellaria
Oceans, in fresh water, and in moist terrestrial habitats, (a few parasitic). 
Ciliary gliding and muscular contractions (circular and longitudinal) provide locomotion though limited
Also includes for now the Acoels which have no digestive tract.

11. Class Trematoda - flukes
all parasitic
flattened, leaf-like body with simple digestive tract
Oral & ventral suckers,
specialize glands for penetration, and encystment.
Typically at least two hosts
the intermediate host is commonly a gastropod mollusk.
In intermediate hosts numerous eggs produced by asexual reproduction.
The definitive host (parasite is the
sexual, adult form) is almost always
a vertebrate.

13. Flukes Infecting Human
Blood flukes – 3 types
Cercariae in water penetrates skin; 200 million infected
S. mansoni
Africa, South and Central America
S. haematobium
Africa
S. japonicum
Eastern Asia
Chinese liver flukes (Clonorchis sinensis)
Eating metacercariae in raw fish; 30 million cases (Eastern Asia)
Lung flukes
(Paragonimus spp.)
Eating metacercariae in raw freshwater crabs, crayfish; several million cases (Asia) – Asia, sub-Saharan Africa, South and Central America
Intestinal flukes (Fasciolopsis buski)
Eating metacercariae on aquatic vegetation; 10 million cases (Eastern Asia)
Sheep liver fluke
(Fasciola hepatica)
Eating metacercariae on aquatic vegetation; widely prevalent in sheep and cattle, occasional in human

14. Intestinal fluke

15. Liver flukes – white-tail deer

16. Class Cestoda - tapeworms
intestinal parasites in vertebrates
Scolex
complex organ of adhesion
variety of suckers and hooks
Proglottids
contains both male and female gonads
break off to regenerate asexually or produce eggs sexually
no gastro-intestinal tract
Ectoderm of tapeworms is covered with tiny microtrichia

17. Class Cestoda - tapeworms
Generally two-host parasites
Pigs, beef and fish are often intermediate hosts for numerous tapeworm species and transmitted to humans by direct consumption. 
e.g. the beef tapeworm Taenia saginatus, can grow to a length of 10 meters, but does not generally pose a threat to health.
The pork tapeworm, Taenia solium is potentially more dangerous, but not when humans are infected as a primary host, but as a secondary host

21. Common Cestodes of Humans
Beef tapeworm
(Taenia saginata)
Eating rare beef; most common of large tapeworms in humans
Pork tapeworm
(Taenia solium)
Eating rare pork; less common than T. saginata
Fish tapeworm (Diphyllobothrium latum)
Eating rare or poorly cooked fish; fairly common in Great Lake region (other raw fish eating)
Dog tapeworm (Dipylidium caninum)
Unhygienic habits of children; moderately frequency
Dwarf tapeworm (Hymenolepis nana)
Juveniles in flour beetles; common
Unilocular hydatid
(E. granulosus)
Cysts of juveniles in humans; infection by contact with dogs (common where humans live with dogs
Multilocular hydatid
(E. multilocularis)
Cysts of juveniles in humans, infection by contact with foxes

22. Class Monogenea Body covered with a syncytial tegument
Without cilia
Leaf-like to cylindrical shape
Posterior attachment organ with hooks, suckers, or clamps
Monoecious
Single host & usually free- swimming
All parasitic
Mostly on skin or gills of fish

23. Ecological Relationship
Free-living flatworms are found exclusively in class Turbellaria
Most are bottom dwellers in marine and fresh water or in moist places on land
Most Monogenea (flukes) are ectoparasites
All Trematodes (flukes) and Cestodes (tapeworms) are endoparasitic