Characteristics of Phylum Platyhelminthes means flat worm Flatworms have three germ layers triploblastic they are the first animal we have discussed in this class with true organs and tissues ID: 935634
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Slide1
Phylum Platyhelminthes and other Acoelomate Animals, Chapter 8, Zoology
Slide2Characteristics of Phylum Platyhelminthes (means “flat worm”)
Flatworms have
three germ layers (
triploblastic
); they are the first animal we have discussed in this class with
true organs and tissues
.
Bilateral symmetry
and
cephalization
.
Flatworms are
acoelomate
, which means the
spaces between the organs
are
filled with mesoderm tissue
called
parenchyma.
Slide3Characteristics of Phylum Platyhelminthes (means “flat worm”)
The nervous system
in flatworms consists
of
anterior
organs
called
ganglia
that
form
a simple brain
.
Excretory system
consists of
two lateral canals connected to structures
called
flame
cells.
They have
no
circulatory or respiratory organs
;
respiration occurs by
simple diffusion.
Slide4Ecology of Flatworms (Platyhelminthes)
Many flatworms
like the
turbellarians
are
free-living
(meaning non-parasitic and not attached to a substrate) organisms that dwell on the bottom of the ocean or freshwater habitats or moist places on land.
All of the flatworms that belong to class
Trematoda
,
Monogenea
,
and
Cestoda
are
parasitic
. Some are
ectoparasites
and others are
endoparasites
.
Many have
complex lifestyles
that
involve more than one host
. The
first host
is usually an
invertebrate
and the
second host
is usually a
vertebrate.
Slide5Digestive System of Flatworms (Platyhelminthes)
The
digestive system
of
most flatworms
is referred to as an
incomplete digestive system
, having only
one opening
that serves as
both a mouth and an anus.
Turbellarians
(such as
planaria
)have a
muscular mouth
and
pharynx
that
protrudes from the ventral surface.
The
pharynx is inserted
into
prey
or
decayed organic matter
, digestive
enzymes are secreted
, and then the
pharynx brings food into the
gastrovascular
cavity
.
Digestion in
Cestodes
(tapeworms
) occurs
by diffusion.
Slide6Digestive System of
Turbellarians
Slide7Excretory System in Platyhelminthes
The
excretory system
of flatworms consists of a
complex network of cells
called
flame cells
connected to canals and tubes.
Flame cells (aka
protonephridia
) are
similar to kidneys
in larger more complex animals (such as the vertebrates).
The flame cells consist of
a hollow cup filled with cilia
that beat and
pump water and nitrogen waste out the body.
When the
cilia
of the
flames cells beat
they
resemble flames
.
Slide8Flame Cells (
Protonephridia
)
Slide9Nervous System of Flatworms
Flatworms are the first animal we have discussed in this class that exhibits
cephalization.
Cephalization
means they
have a head (anterior) and tail (posterior) region and a brain.
Cephalization
allows animals to move
(crawl, swim, fly etc.)
in a certain direction
to search for resources.
In order to make decisions, an animal requires intelligence from a
central nervous system (brain
or ganglia)
.
Slide10Nervous System of Flatworms
The
central nervous system
in flatworms is a
region of nerve tissue
at the
anterior end
called a
ganglion.
The
ganglion
attaches to
a pair of ventral nerve cords
that
run the full length of the body.
The
nerve cords
are sensitive to
touch, chemical detection, balance (equilibrium), water current direction
and they
can control muscular movement.
The
ganglia are also attached
to
eye spots
that are
sensitive to light
(but they can not form images).
Slide11Nervous System of Flatworms
Slide12Reproduction of Flatworms
Flatworms reproduce both
sexually
and
asexually.
Sexual reproduction
usually occurs by
cross fertilization (exchanging sperm)
with other
hermaphrodites
.
Most
flatworms are
monoecious
. (both male and female)
Only
a few
flatworms are
dioecious
(separate sexes).
Asexual reproduction
occurs by
fission
. The organism
separates into two halves
that
regenerate into two adults.
Slide13Regeneration of a Planarian Flatworm
Slide14Class
Turbellaria
Free-living
, soft, flat bodies
Bodies
are
covered in cilia
Mouth
located on
ventral surface
near the
center of the body
Mostly hermaphroditic
Some
can
reproduce asexually by fission
Examples:
Dugesia
(
planaria
),
Microstomum
,
Planocera
Slide15Class
Turbellaria
; Genus
Dugesia
,
common name
Planaria
Slide16Class
Trematoda
; Subclass
Digenea
Digenetic Flukes
Parasitic
lifestyle with
two hosts.
First
intermediate host
is a
mollusk
.
Second
definitive host
is a
vertebrate.
Sexual reproduction
occurs in the
definitive host.
Occasionally
a
third host
(intermediate) plays a role in the life cycle.
Parasitism can occur in almost every system of the body
including the digestive, respiratory, circulatory, excretory, and reproductive systems.
Examples:
Fasciola
,
Clonorchis
,
Schistosoma
Slide17Class
Trematoda
, Subclass
Digenea
Slide18Class
Trematoda
; Subclass
Digenea
Digenetic Flukes
A
typical life cycle
would include the following life cycle stages;
adult, egg,
miracidium
,
sporocyst
,
redia
,
cercaria
,
and
metacercaria
.
Egg
is
released from the host's excrement
and
must reach a source of water to be released.
In the water the
egg releases a free-swimming, ciliated larva
called the
miracidium
The
miracidium
penetrates and enters the tissues of a mollusk
, and
transforms
into a
sporocyst
.
Slide19Class
Trematoda
; Subclass
Digenea
Digenetic Flukes
Sporocysts
then
reproduce asexually
to produce
redia
.
Redia
reproduce asexually
to produce
cercaria
.
Cercaria
emerge from the mollusk
and
penetrate a second intermediate host
or
they can develop
as a
metacercaria
on
vegetation or in
the
animal host.
Metacercaria
are eventually
ingested by a definitive host
and
develop into adult flukes.
Slide20Trematoda
(Flukes)
Slide21Fluke Life Cycle
Slide22Parasitic Flukes in Humans
Some
of the
most serious parasites
in
humans are flukes
.
Clonorchis
is a
liver fluke
that is common in
China
,
south Asia
, and
Japan
and can cause
cirrhosis of the liver and death.
Schistosoma
is a
blood fluke
that causes a serious infection called
schistosomiasis
. Schistosomiasis is
one of the most deadliest diseases in the world
.
There is estimated to be about
200 million people infected
with
schistosomiasis
in
Africa, South America, and the Middle East.
Symptoms
of schistosomiasis include
dysentery, anemia, enlarged
liver, bladder inflammation
and brain damage.
Slide23Person infected with Schistosomiasis
Slide24Parasitic Flukes in Humans
One type
of
fluke that infects birds
causes a
painful irritation
in
humans
called
swimmer's itch
.
In the case of this fluke occurring
in humans, the life cycle becomes terminated
since the
host in unsuitable
.
Children with Schistosomiasis
Swimmer's itch
Slide25Class
Monogenea
; Monogenetic Flukes
Ectoparasites
that
attach to the gills of fish.
Hook-like mouth
called an
opisthaptor
.
Occasionally
they are
found in the urinary bladders of frogs and turtles
, but
mostly on the skin or gills of fish
.
A certain kind even lives in the eye of a hippopotamus.
Common but
cause little damage to their host
.
They
can become a serious threat when fish become crowded
, like in the case of
fish farming.
Life cycle simple
with only a
single host
Examples:
Dactylogyrus
,
Polystoma
,
Gyrodactylus
Slide26Monogenea
Image on the right found on the gills of a fish
Slide27Class
Cestoda
(Tapeworms)
Long flat bodies
with a
hook-like mouth
called a
scolex
. The
scolex
is used for attaching to the intestinal wall of it’s host.
The
rest of the body
is followed by
regular repeating units
of
reproducing sections
called
proglottids
.
The
main body
of a
tapeworm
is a
chain of
proglottids
called a
strobila
.
No digestive tract.
Nutrients
are
absorbed across the skin
by
diffusion.
Slide28Tapeworm Anatomy
Slide29Class
Cestoda
(Tapeworms)
All tapeworms
require at least two hosts.
Adults are parasitic
in the
digestive tract of vertebrates.
Almost
ALL
vertebrate species
can
become infected
, but
adult
tapeworms
do very little harm to their hosts.
Humans
often
get infected
by
consuming raw
or
rare beef, pork, or fish (larva form cysts in the muscle tissue).
Children
often
become infected
by
putting their fingers in their mouth
after
touching infected animals.
Slide30Class
Cestoda (Tapeworms)When the larva
are
ingested
by
an
intermediate
host
(cattle, pigs, dogs etc.) then the larva can
migrate to the skeletal muscle
where they become
larval cysts
called bladder worms (cysticerci)
Occasionally larval cysts (called bladder worms)
can develop in the brain
leading to
severe brain damage
and
death
(
cerebral
cysticercosis
).
Slide31Pork Tapeworm Life Cycle
Slide32Beef Tapeworm Life Cycle
Slide33Tapeworm
Slide34Tapeworm
Scolex
Slide35Proglottids
Slide36Phylum
Nemertea
(Ribbon Worms) and Phylum
Gnathostomulida
(Jaw Worms)
Ribbon Worms
and
Jaw Worms
are
similar to animals in the Phylum Platyhelminthes
in several ways,
but have some important differences
,
placing them in their
own phyla
.
Both
are
acoelomate
and
bilaterally symmetrical
.
Ribbon worms
have
flame cells
and
ganglia.
Some ribbon worms
can
regenerate
like planarians.
However,
unlike flatworms
,
ribbon worms
have a
complete digestive tract
with
both
a
mouth and an anus.
Ribbon worms
also have a
circulatory system.
Jaw worms
are a
newly discovered species
and have
yet to be properly classified.
They do
somewhat resemble rotifers
.
Slide37Ribbon Worms and Jaw Worms
Ribbon Worms
Jaw Worms