Phylum Platyhelminthes
Flatworms
Flukes
Tapeworms
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Phylum Platyhelminthes
Phylum Platyhelminthes
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The phylum consists
of four classes
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Turbellaria
Trematoda
Cestoda
Triclad Flatworm
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Phylum Platyhelminthes
Reproduction
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Almost all are simultaneous
hermaphrodites
Parasitic species (flukes and
tapeworms) have complex
lifecycles, with various hosts
and several different larval
stages
Incredible powers of
regeneration
Phylum Platyhelminthes
Nervous System
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Free-living species usually have a
well-developed sensory system
Parasites generally have less
elaborate systems.
WHY?
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Phylum Platyhelminthes
Taxonomic Summary
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Phylum Platyhelminthes
(Flatworms)
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Class Turbellaria
Class Cestoda
Class Trematoda
Class Monogeneans
Phylum Platyhelminthes
Class Turbellaria
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Most are free–living,
tiny and
inconspicuous
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Primarily marine and
freshwater
Free-living
Flatworm
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Phylum Platyhelminthes
Flatworm Body Plans
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Exhibit bilateral symmetry, acoelomate, and are
triploblastic
Parenchyma tissue
Phylum Platyhelminthes
Digestion and Excretion
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Mouth is usually located
at the anterior end or
mid-body on ventral
surface
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Excretory system
– Contains flame
bulbs
Phylum Platyhelminthes
Regeneration
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Many species posses remarkable powers of
regeneration and repair wounds
Phylum Platyhelminthes
Turbellarian Lifestyles
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Most are benthic
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Posses several nerve cords with a centralized
ganglia (brain)
Phylum Platyhelminthes
Turbellarian Habits
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Some species also have a protrusible pharynx that
captures food and transfers it into the mouth
– Can be carnivores or scavenge on dead animals and
detritus
Phylum Platyhelminthes
Reproduction
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Reproduction occurs
with the reciprocal
exchange of sperm
Fertilized eggs are
released and usually
develop directly into
flatworms
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Muller's larva
Phylum Platyhelminthes
Class Cestoda (Tapeworms)
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Defining
characteristics
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Scolex
Proglottids
Phylum Platyhelminthes
Proglottids
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Proglottids
– Each animal can be
3,000 – 4,000 per
animal
– Amazing reproductive
output
– Each may contain
several ovaries and
1,000 distinct testes
Phylum Platyhelminthes
Beef tapeworm
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Phylum Platyhelminthes
Problems of a parasitic existence
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Reproduce within the definitive host
Get fertilized eggs out of the host
Contact a new and appropriate host
Obtain entrance into the host
Locate the appropriate environment within the host
Maintain position within the host
Withstand an often anaerobic environment
Avoid digestion or attack by the hosts immune system
Avoid killing the host, at least until reproduction is
completed
Phylum Platyhelminthes
Class Trematoda (Flukes)
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All are external and
internal parasites of
other animals
Leech-like bodies with a
sucker at each end
Have a gut and welldeveloped reproductive
system, never
segmented
Phylum Platyhelminthes
Trematoda Lifecycles
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The lifecycle is
complex with up to 4
different hosts and
several larval types
Phylum Platyhelminthes
Trematodes of Concern
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Schistosomiasis
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Deadly prominent disease in
many regions of the world
Bores into the skin of the
definitive host and travels in
the circulatory system to the
heart the lungs and the
kidneys where it feeds and
grows
Inflammation is caused by
eggs becoming trapped in the
hosts tissues
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Chinese liver fluke
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Lives in the bile duct of
humans, cats, and dogs
(1-2 cm.)
Goes through two
intermediate hosts
Infection occurs from
ingestion of raw fish
Phylum Platyhelminthes