Transcript PowerPoint 10: Platyhelminthes 2

Invertebrate Zoology
Lecture 10: Phylum Platyhelminthes
Part 2
Lecture outline
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Phylum Platyhelminthes
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Asexual reproduction/regeneration (Class
Turbellaria)
Sexual reproduction (Class Turbellaria
Life cycles: Class Monogenea
Life cycles: Class Trematoda
Life cycles: Class Cestoda
Life cycles: Wrap-up discussion!
Asexual reproduction/
regeneration: Class Turbellaria
 Transverse fission
Note eye
development in each
section
Develop  separate
Asexual reproduction/
regeneration: Class Turbellaria
 Capacity for regeneration
Transverse cuts  new
individuals
 Capacity to regenerate is
greatest at head (Planaria)
 Polarity maintained
 Undifferentiated
mesenchyme cells 
particular cell types
Capacity depends on
body position
Asexual reproduction/
regeneration: Class Turbellaria
 Capacity for regeneration
Longitudinal cuts
 Multiple heads
 Multiple tails
Sexual reproduction
Class Turbellaria (Planaria focus)
 Reproductive systems
Hermaphroditic
Multiple testes and ovaries
Many variations
Male/female openings
 Common vs. one for each
 Planaria: common opening
Sperm have two tails!
Sexual reproduction
Class Turbellaria (Planaria focus)
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Mating
 Penis everts during mating
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Stored retracted in “male atrium”
Opening sometimes in mouth: Orogenital pore
 Internal fertilization  Sperm travel via
oviducts to ovary
Sexual reproduction
Class Turbellaria (Planaria focus)
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Mating (cont.)
 If no female opening  hypodermic
impregnation (a.k.a. penis fencing)
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Eggs travel through body to ovary.
Sexual reproduction
Class Turbellaria (Planaria focus)
 Fertilization
In ovary
Return trip via oviducts
 Yolk deposited
Eggs encapsulated & released
or brooded in “uterus”
 Summer vs. resting eggs
Difference?
 Direct development or larvae
Life cycles: Class Monogenea
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Single host
Sample life cycle 1: Dactylogyrus
vastator, a gill parasite of carp
 Adult: on gills
 Fertilized eggs  encased zygotes
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Drop to substrate, hatch into…
 Oncomiracidium
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Swimming form
 Host attachment  Maturation
Dactylogyrus vastator, a gill
parasite of carp
Life cycles: Class Monogenea
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Sample life cycle 2: Polystoma
integerrimum, a parasite of frogs
 Basic stages similar to Dactylogyrus
 Key: Two variations tied to host life cycle
 Young tadpoles as host
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Larvae attach to external gill
Rapid life cycle
 Older tadpole as host
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Larvae attach to external gill of tadpole
Migrate to bladder after frog metamorphosis
Mature after ~2-3 years in response to frog sex
hormones
Polystoma integerrimum
Life cycles: Class Trematoda
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Example: Chinese liver
fluke, Clonorchis sinensis
 Overview
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Definitive hosts: Humans and
other carnivorous mammals
Causes liver disease &
associated symptoms
Two intermediate hosts
 Intermediate host 1 = snail
 Intermediate host 2 = fish or
crustacean
How does the infection occur?
Life cycles: Class Trematoda
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Clonorchis sinensis: life stages
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Egg
Miracidium
Sporocyst
Redia
Cercaria
Metacercaria
Adult
From Pearse & Buchsbaum, Living Invertebrates
Life cycles: Class Trematoda
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Clonorchis sinensis: life cycle (in hosts)
From Pearse &
Buchsbaum, Living
Invertebrates
Life cycles: Class Cestoda
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Anatomy of a proglottid
 Hermaphrodites
 Most mature/functional systems in posterior
proglottids
 Fertilized eggs stored in posterior proglottids
 Eggs released or proglottids break off  feces.
Life cycles: Class Cestoda
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Example: Beef tapeworm, Taenia
saginata
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Proglottid with zygotes
Onchospheres
Cysticercus
Maturation
Reproduction
Parasite life cycle wrap-up
 Advantages of multiple hosts?
Think carefully about life cycles presented!
 Disadvantages of multiple hosts?
Think carefully about life cycles presented!
How are life cycles “broken”?
 Mechanisms to insure transfer
Example 1: Killfish infected by trematodes
Example 2: Particular snails infected by
trematodes