Life Cycles of Digenetic Trematodes Chapter 15, p' 230237

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Life Cycles of Digenetic Trematodes Chapter 15,
p. 230-237
Digenetic trematodes use 2 or 3 hosts in their
life cycles.   FIRST INTERMEDIATE HOST is always
a ___________________________. Reproduction
? SECOND INTERMEDIATE HOST may occur in some
life cycles. This host is an
__________________________________________________
___ Reproduction? DEFINITIVE HOST is a
_________________________________.
Reproduction? 
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Life Cycles of Digenetic Trematodes
As many as _______________________________________
______ have been recognized in digenetic
trematode life cycles. - Many
variations occur - not all 6 larval stages may be
present within a species.
- Life cycles have been difficult to elucidate
due to all these larval
stages.   Today I will discuss a generalized
trematode life cycle.   We will examine the
specific life cycle of each trematode of medical
and veterinary importance when we get to each one
in lecture and lab.  
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Generalized Life Cycle
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Adult
ADULT occurs in the definitive host Although
most adults are _____________________________. Met
hod of fertilization? Sexual reproduction
involving gamete formation (oocytes and
sperm) followed by fertilization results in the
formation of thousands of fertilized
eggs.
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Egg Ovum
After fertilization and eggshell formation in the
ootype, eggs move through the uterus. As they
move through the uterus, 2 processes occur 1.
______________________________ - eggshell is
hardened into a tough protein called
______________________ as the egg passes along
the uterus. - function?  
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Egg Ovum
2. ________________________________________-
mitosis of the zygote to form the embryo. 
- If the embryo is fully differentiated
into a miracidium before the egg
is released from the adult, an __________________
_______________is produced.  - If
the embryo consists of a number of
undifferentiated cells when the
egg is released, an _____________________________
____is produced.
embryonated egg
unembryonated egg
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Egg Ovum
Eggs are ejected from the adult by the
_____________________________
through the
common genital pore. Eggs leave the definitive
host via _______________________________
____________
(depending on the species) and are generally
deposited into
an aquatic environment. Hatching of the egg may
occur 1. or 2. Hatching of the egg involves
the
opening of an
______________________________

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Miracidium
Ciliated embryo that hatches from the
egg Miracidia that hatch in water
In some species, the egg is ingested by the
snail and the miracidium hatches within the
snail
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Miracidium
Morphology Small, elongate organism covered
by __________________________   At anterior end
is the _________________________ that
functions in contacting the snail intermediate
host. The apical papilla contains
openings from ____________________________________
_. When a snail is contacted, the penetration
glands secrete enzymes to aid in embedding the
miracidium within the snail's tissues.
___________________________ are common for
photoreception. A mass of
______________________________ lies in the
posterior end. These cells divide asexually to
form the next larval generation.
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Miracidium
Upon entering a snail, the miracidium loses its
cilia and transforms into a sac-like body called
the __________________________________________

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Sporocyst
Upon entering a snail, the miracidium loses its
cilia and transforms into a sac-like body called
the MOTHER SPOROCYST. Mother sporocysts occur in
the snail at the site of penetration. Mother
sporocysts consist of a __________________________
_____ surrounding developing ____________________
___________ mouth or digestive tract?

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Sporocysts
In some digenetic trematodes, the germ cells in
the mother sporocyst divide asexually to give
rise to another generation of sporocysts called
________________________. Mother sporocyst
bursts to release these daughter
sporocysts.   In other trematodes, the germ cells
of the mother sporocyst form a new larval stage
called the ______________________________  
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Redia
Mother rediae burst out of the mother sporocyst
and migrate to the _______________________________
___________________________of the snail host.

hepatopancreas
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Redia
Each redia contains a __________________________
and short ___________________________ What do
they feed on? ________________________ in the
mother rediae may develop into a second
generation of rediae called ______________________
_______or may develop into _______________________
______.
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Cercaria

• CERCARIAE leave the sporocyst or redia, migrate
  out of the snail, and become _____________________
  _____.
• Morphology
• 1. Cercarial body is an _________________________
  _____
• - oral sucker and acetabulum are present
• - digestive tract is complete
• excretory system is developed
• many types of gland cells are present
• 2 eyespots are common
• no reproductive structures

Microcercous cercaria
Furcocercous cercaria
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Cercaria

• 2. _____________________________ used for
  swimming.
• - may be unbranched with or without fins
• - tail characteristics important in
  identification
• Type of cercaria is based on characteristics of
  the body and tail. We will look at 3 types
• Furcocercous type forked tail
• Gymnocephalous type straight tail
• Microcercous type short tail

Microcercous cercaria
Furcocercous cercaria
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Cercariae may (1) penetrate the definitive
host (schistosomes) (2) penetrate a second
intermediate host and encyst as metacercariae,
or (3) attach to aquatic vegetation and encyst as
metacercariae.    
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Metacercaria

• METACERCARIA is formed as a cercaria loses its
  tail and encloses itself in a ____________________
  ____________
• Cyst is formed by
• 2.
• Metacercaria is an ______________________________
  
• Reproductive organs may begin to form but eggs
  are never produced.
•  
•  
•  
•  
•  

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Metacercaria
Metacercariae may occur within a second
intermediate host or on aquatic vegetation. They
are viable for weeks to years. When the second
intermediate host or aquatic vegetation
containing metacercariae is eaten by a definitive
host, the metacercaria ___________________________
__in the digestive tract and matures to the
____________________________.