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Flatworms
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Phylum: Platyhelminthes
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3 Germ layers
Bilateral symmetry
Acoelomates: No body cavity
Results in thin, flat bodies
 Low surface area:volume ratio
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Gastrovascular Cavity
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Nutrients/Waste enter/exit same location
Divided into three classes
Turbellaria
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Majority are marine species
Often called planarians
Aquatic scavengers
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Very simple digestive system
Free living, so they need to breakdown their
own nutrients
Few live in freshwater
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Must excrete excess H2O
Uses excretory tubule system shown in 36-2
Trematoda
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Called Flukes
Mainly parasitic
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Attach to the host by a sucker
Draws body fluid of host into the fluke
Tegument
Outer portion of the fluke
 Protects against the host’s
immune/defense stystem
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Fluke Reproduction (36-4)
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Complex life cycle
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Different host at different points in life cycle
Primary Host
 Host that the adult lives in
 Consumes nutrients
 Reproduces
Intermediate Host
 Larval stage of development
 Larva get nourishment
 Used to get back to the primary Host
Cestoda
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Tapeworms
Intestinal parasites
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Tegument similar to flukes
Scolex used to attach to the host
Body segments called proglottids
Grows by adding segments
 Some may have over 2000 (over 30 ft)
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Completely lack digestive organs
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Absorb directly from host
Cestoda Reproduction
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Complex life cycle similar to flukes
Proglottid contains eggs
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Proglottid breaks off
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Carries eggs away in feces
Vegitation contaminated by feces
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Eggs fertilized by other segment on same
worm, or different worm in same host
Consumed by herbivore
Eggs develop into larva in intermediate host
Get to muscle and form cyst
Primary host consumes animal muscle
Phylum: Nematoda
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Roundworms
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Long,slender, tapered at anterior and
posterior ends
Pseudocoelomates
Complete digestive tract
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2 openings
Covered by a cuticle:used for
protection
Free living and parasitic
Ascaris
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Intestinal parasite
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Enter body through contanimated food
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Pig, human, horse
May block intestinal tract
Eggs carried out in feces
Egg  Larva in intestine
Larva  Bloodstream
Bloodstream  Lungs/throat
Lungs/Throat  Outside body(cough),
intestine(swallowed)
Hookworm
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Intestinal parasite
Remove blood
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Can cause anemia
Eggs released through feces
Eggs develop into larvae in soil
Larvae burrow into foot
Get into bloodstream
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Follow similar path of ascaris
Trichinella
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Embed in intestinal walls
Larvae enter bloodstream, go to
muscle, form cyst
Consumed in undercooked meat
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Mainly pork  ALWAYS WELL DONE!!!
Causes trichinosis
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Muscle pain/stiffness
If in heart = death
Pinworm
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Most common in US (16% adult,
30%children)
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Do not cause major illness
Intestinal
Eggs deposited outside anus
Eggs picked up, moved to other
locations
Ingested eggs end up back in intestines
Filarial Worms
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Tropical Parasites
Some live in lymphatic system
Transferred by mosquitoes
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Can completely block lymphatic vessels
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Mosquito is intermediate host
 Where the larvae develops
Transfer to new host
Causes elephantiasis
Also what causes heartworm in dogs