Phylum Platyhelminthes

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Phylum Platyhelminthes
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Phylum Platyhelminthes
20,000 species. Bilateral symmetry. Flattened
dorso-ventrally. Triploblastic.
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Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Small flatworms with no permanent gut
cavity. Free-living, marine and brackish water.
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Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Order Tricladida
Gut with three branches. Marine, freshwater, and
terrestrial.
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Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Order Tricladida
Order Polycladida
Gut with many branches. Large marine
flatworms. Often brightly colored.
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Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Order Tricladida
Order Polycladida
Class Monogenea
Monogenetic flukes. Most are ectoparasites. Hooks
on both ends to attach to host.
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Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Order Tricladida
Order Polycladida
Class Monogenea
Class Trematoda
Digenetic flukes. Most are endoparasites. Suckers
to attach to hosts.
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Phylum Platyhelminthes
Class Turbellaria
Order Acoela
Order Tricladida
Order Polycladida
Class Monogenea
Class Trematoda
Class Cestoda
Tapeworms. Endoparasites. No digestive tract.
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TurbellariansWhat do they look like?
Fig. 2
Head region with a cerebral ganglion and sense
organs. Elaborate reproductive systems
simultaneous hermaphrodites. Protonephridia for
osmoregulation in freshwater species. Muscular
system allows for complex movements.
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TurbellariansWhat do they look like?
Fig. 5
Ciliated epidermis. Basement membrane adds
support. Muscular antagonistic system. Rhabdites
in mesenchyme produce rhabdoids.
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TurbellariansHow do they support themselves and
locomote?
Hydrostatic mesenchyme and muscular antagonistic
system. Crawl using cilia and mucus
secretion. Nerves can be ladder-like with a
cerebral ganglion.
Fig. 18
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TurbellariansHow do they support themselves and
locomote?
Fig. 18
Sense organs tactile, chemical, water flow,
light, orientation in space.
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TurbellariansHow do they feed themselves?
Fig. 11
acoels
triclads
Carnivorous or scavengers. Pharynx simple or
complex. Complex are eversible.
polyclads
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TurbellariansHow do they feed themselves?
Fig. 13
acoels
rhabdocoels
triclads
polyclads
Gut simple or complex. Partially digested food
transferred throughout gut then taken up by
gastrodermis.
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TurbellariansHow do they osmoregulate?
Protonephridia in freshwater species. Fluid drawn
into flame bulbs, ions reabsorbed water excreted,
fluid leaves through nephridiopores.
Fig. 16
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TurbellariansHow do they reproduce and develop?
Asexual reproduction.
Transverse fission. Able to regenerate lost body
parts.
Fig. 21
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TurbellariansHow do they reproduce and develop?
Sexual reproduction Simultaneous hermaphrodites
Fig. 22
Male structures testes drain into sperm ducts
which leads to a seminal vesicle for sperm
storage. Prostatic glands supply seminal fluid.
Cirrus (or penis) for sperm transfer.
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TurbellariansHow do they reproduce and develop?
Sexual reproduction Simultaneous hermaphrodites
Fig. 22
Female structures germovitellarium produces eggs
and yolk together (endolecithal eggs). In
others, eggs produced in ovary and yolk added
later by yolk gland (ectolecithal eggs). Female
atrium often has seminal receptacles or
copulatory bursa to store received sperm.
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TurbellariansHow do they reproduce and develop?
Fig. 23
Simultaneous transfer of sperm. Zygotes either
retained in adult uterus or laid in encapsulated
eggs.
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TurbellariansHow do they reproduce and develop?
Some turbellarians have indirect development that
includes Mullers larva.
Fig. 24
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Monogenea and TrematodaWhat do they look like?
Fig. 3
Endo- and ectoparasites. Oval or leaf shaped with
external attachment structures. Simultaneous
hermaphrodites.
Monogenetic fluke
Digenetic fluke
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Monogenea and Trematoda What do they look like?
Fig. 7
Tegument provides protection and aids in gas
exchange.
No cilia. Move using muscular action.
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Monogenea and Trematoda How do they move and
adhere?
Monogenetic flukes have attachment organs at both
ends. Prohaptor at oral end with suckers,
opisthaptor at hind end with barbed suckers.
Fig. 8
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Monogenea and Trematoda How do they move and
adhere?
Digenetic flukes have an oral sucker at oral end
and an acetabulum on ventral surface.
Ladder-like nervous system. Suckers have tactile
sensors.
Digenetic fluke
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Monogenea and Trematoda How do they feed
themselves?
Feed on host tissues by pumping of muscular
pharynx. Gut with two cecae lined with cells for
nutrient uptake.
Monogenetic fluke
Digenetic fluke
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Monogenea and Trematoda How do they osmoregulate?
Fig. 15
Same basic structure as Turbellarians.
Digenetic flukes have slightly different
configuration of plumbing.
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Monogenea and Trematoda How do they reproduce
and develop?
Simultaneous hermaphrodites with mutual cross
fertilization. Eggs are ectolecithal and can be
brooded for long time. Indirect development with
one or more free living larval stages.
Fig. 28
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Monogenea and Trematoda How do they reproduce
and develop?
Fig. 30
Monogentic flukes have one host. Adult releases
encapsulated embryos which hatch into the first
larval stage (oncomiracidium). They are ciliated
and swim until they locate another host. Larva
metamorphoses into a juvenile fluke.
Fig. 29
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Monogenea and Trematoda How do they reproduce
and develop?
Fig. 31
Digenetic flukes have more than one host. Eggs
produced by adults in definitive host. Eggs eaten
by intermediate host or hatch into free-swimming
larva called miracidia which actively penetrates
intermediate host. Several asexual generations of
larvae are produced which finally produce
afree-swimming larva called a cercaria. They
encyst into a metacercaria. Metacercaria are
consumed by the definitive host.
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CestodesWhat do they look like?
Fig. 4
A scolex attaches them to the inside of their
host followed by a neck and a strobila (long
segmented trunk). Individual segments are
proglottids.
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Cestodes What do they look like?
Fig. 7
Tegument has microscopic folds (microtriches) to
increase surface area. Microtriches
interdigitate with host villi to aid nutrient
absorption.
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Cestodes How do they adhere and move?
Dont move much. Adhere with scolex aided by
microtriches. Scolex is well innervated.
Longitudinal nerve cords run down length of
animal.
Fig. 9
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Cestodes How do they feed themselves?
Fig. 7
No gut. Nutrient uptake (both pinocytosis and
diffusion) across tegument with microtriches.
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Cestodes How do they osmoregulate?
Protonephridia with long excretory ducts leading
to an opening in the posterior proglottid.
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Cestodes How do they reproduce and develop?
Fig. 4
Simultaneous hermaphrodite with mutual
cross-fertilization. Can self-fertilize.
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Cestodes How do they reproduce and develop?
Fig. 32
Complete male and female structures in each
proglottid. Eggs are fertilized and stored in
uterus which expands to fill proglottid. Proglotti
ds break free and are excreted with host feces.
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Cestodes How do they reproduce and develop?
Usually involves more than one host. Variable
life cycles. Proglottid drops off and is excreted
by definitive host. zygotes develop in
environment. Zygote is ingested by second host
and it encysts in tissues which are consumed by
the definitive host.
Fig. 33