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Phylum Platyhelminthes
Zoology WCHS
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Phylum Platyhelminthes
• Flat worms
• Triploblastic= 3 tissue
layers
• Acoelomate
• Bilateral symmetry
• Hermaphroditic
• 1 opening for digestion
• Simple nervous and
muscular systems
• Flame cells
• May be free living or
parasitic
• CEPHALIZATION
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Acoelomate
Ectoderm
Mesoderm
Endoderm
Digestive cavity is the only inner cavity
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Phylum Platyhelminthes: Class Turbellaria
Acoelomate
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Other Body Plans:
Pseudocoelomate
Ectoderm
Mesoderm
Endoderm
Fluid filled cavity between the endoderm and ectodermpseudocoelom
Differs from a true coelom because….
• It is not entirely lined with mesoderm tissue
• Organs are not suspended or attached to membranes
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(mesenteries)
Other Body Plans:
Coelomate
Ectoderm
Mesoderm
Endoderm
Epithelial lined cavity between digestive
tract and body wall
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Flatworm Body Systems
• No Circulatory or
Respiratory systemssimple diffusion through
body wall
Systems Present•
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Digestive
Nervous
Excretory
Reproductive
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Flatworm Body Systems:
Digestive
Incomplete•
mouth
•
pharynx (to swallow food)
•
intestine(no anus)
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Nervous System
Lateral nerve cord
anterior ganglion
sensory receptors
transverse nerve cord
Eye spot= detects
light
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Cephalization=“Primitive Brain”
Auricle
Cerebral
ganglion
Paired
nerve cords
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Excretory System
-Gets rid of
nitrogenous wastes
- protonephridia- first
kidney
Components:
-Flame cells
-Excretory ducts/tubes
-pores
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Reproductive System
•Sexual and asexual
reproduction
sexual- eggs + sperm
asexual- regeneration
•Hermaphroditesboth male (penis and
testis)
and
female organs(vagina
and ovary)
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Kingdom Animalia
Phylum Platyhelminthes
Classes:
Turbellaria
Trematoda
Cestoda
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Class Turbellaria
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•
•
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Most free-living
Aquatic
Eye spots
Regenerate if cut
in two
• Ex. Planaria
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Planarians
• Free-living flatworm
• bilateral symmetry
• Lives in fresh water
usually under leaves
and rocks
• Usually feeds on
dead or slow moving
organisms
Planarian Reproduction
Reproduction:
• Sexually:
hermaphrodites
each Planaria
gives and
receives sperm
• Asexually: can
regenerate missing
body parts (called
fission)
Detaches its tail
end and each
half regrows the
lost parts
What would happen ????
Planarians: body structures
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Nervous/sensory system: Brain-like structure
Nerve cord: carries impulses down body
Eyespots: sense light and dark
Sensory pits: line sides of head to aid in
movement and sensing surroundings
• Flame Cells: remove excess water and
nitrogenous wastes
Planarians: body structures
Digestive/excretory system
eyespot
• Mouth: located in center of
ventral side
• Pharynx: tube like
structure which extends
from mouth during feeding;
acts like a straw sucking
up food and carrying it to
body
• Food enters mouth and
solid wastes exit mouth
ganglion
ganglion
Gastrovascular
cavity
Mouth
Nerve
cord
pharynx
Flame cells
LABEL YOUR PLANARIAN!!!
Class Trematoda
• Parasites
• Holdfast devices
– Endoparasites
• Complex life cycle- larval
stage in one or more hosts
Primary host-juvenile/larva
stagesexual reproduction
Secondary host- adult stage,
asexual reproduction
Ex. Blood and liver flukes
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Flukes
Blood fluke life cycle:
• Eggs are released in water
from wastes of infected host
• Hatch in to swimming larvae
in water
• Larvae enter a host (like a
snail) where they develop &
mature
• Enter water again and bore
into skin of new host (man)
• From the blood stream they
bore into intestines where
they attach and feed on
blood
Schistosoma
• Blood flukes
• 200 million people
• 1 million deaths/year
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Life Cycle of a Schistosome Fluke
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Schistosome
• Cercaria have forked
tail
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Swimmers Itch
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Clonorchis sinensis
human liver fluke
Oral sucker
Intestine
Uterus
Yolk gland
Ovary
Seminal
recepticle
Testes
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Clonorchis sinensis
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Chinese liver fluke
50 million people
Cirrhosis of liver
Diarrhea
Edema
Pain
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Fascioloa hepatica
• Sheep liver fluke
• Sheep, cattle and
man
– Weight loss
• Eat contaminated
vegetation
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Life Cycle of the Sheep Liver Fluke
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Paragonimus westermani
• Lung fluke
• Carnivores, pigs,
rodents and man
• May be fatal
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Class Cestoda: “cess pool”
• Tape worms
• All parasitic
• Live in intestines of
vertebrates
• No digestive system
• 40 feet long
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Tapeworm structures
• Scolex= head
• hooks and suckers to
aid in attachment to
intestine
• Proglottids: individual
parts of worm
– Each one is detachable
– Each proglottid may
contain up to 100,000
eggs which fall off when
full
– When released, they exit
with the host’s wastes
Tapeworm life cycle
• Eggs hatch in intestines of
intermediate host (pig or cow)
• Young worms burrow out of
intestine into pig’s muscle
tissue forming cysts
• Secondary host (man) eats
undercooked/raw meat
containing worm larvae cysts
• Larvae hatch and mature in
intestines
• Attach to intestines, soak up
digested food of host
• May enter bloodstream and
infect other tissues
Scolex
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Proglottid
Testes
Uterus
Vas deferens
Seminal receptacle
Ovary
Yolk gland
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Pork Tapeworm (Taenia solium)
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Taenia
saginata
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Life Cycle of the Broad Fish Tapeworm
Diphyllobothrium
latum
Source: Redrawn From Centers for Disease Control, Atlanta, GA.
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Dipylidium caninum
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Echinococcus granulosus
• Parasite of dogs
– Host
• Juveniles in sheep,
man and other
mammals
– Intermediate host
• Hydatid cyst
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Hydatid Cyst
• Cysticercus
– Juvenile stage
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Ecinococcus granulosus
• Adult stage in dog
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