Phylum Platyhelminythes by MikeJenny

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									Phylum Platyhelminythes
Platyhelminthes

 ~ 20,000 extant species
 Parasitic + free-living
 Unsegmented flatworms
    Platyhelminthes
   Triploblastic, acoelomate, bilaterally
    symmetrical
   Incomplete gut; absent in some parasitic forms
   Cephalization of nervous system
   Protonephridia: excretion and osmoregulation
   Hermaphroditic
Support

   Hydrostatic skeleton

   Elastic body wall

   Body musculature
Taxonomy

   Class Turbellaria

   Class Monogenea

   Class Trematoda

   Class Cestoda
    Class Turbellaria

– Free-living flatworms

– Most are aquatic

– Epidermis cellular and ciliated
Feeding and digestion in
Turbellaria
   Consume invertebrates (few herbivores and
    omnivores)
   Locate food via chemoreception
   A few are symbiotic
Turbellaria digestive system

   Mouth, pharynx, intestine = incomplete gut
   Pharyngeal glands produce mucus and
    proteolytic enzymes
   Digestion extracellular, then phagocytization
    in intestine
    Turbellaria nervous system
   Sense organs
    – Tactile receptors cover body -
      concentrated anteriorly
    – Chemoreception = location of food
    – Statocysts = gravity detection and
      orientation
    – Photoreceptors
       Inverted pigment cup ocelli
       Negative phototaxis
Turbellaria nervous system
   Variable: simple net-like to cephalized & bilateral

   Ladder-like NS = more recently evolved
    Class Monogenea

   Monogenetic flukes (life cycle = one host)
    – Body covered by tegument
    – Oral sucker reduced or absent
    – Ectoparasitic (usually fish)
    Class Monogenea

   Monogenetic flukes (life cycle = one host)
    – Eggs hatch into ciliated larvae = oncomiracidia
    – Mature and find host
Class Trematoda

   Digenetic flukes (multiple hosts)
    – Body with tegument
    – One or more suckers present
    – Internal parasite
Fluke Digestive System
   Feed on host tissues and fluids (muscular
    pharynx)
    – Or, material in host gut

   One-way digestive tract: mouth, muscular
    pharynx, short esophagus, intestinal cecae
Fluke Nervous System
     Ladder-like
     Cerebral ganglion
     Suckers with tactile receptors (bristles
      and spines)
Sexual repro flukes

   Hermaphroditic
   Mutual cross fertilization
   Male structures
    – Variable testes
        Monogenetic = many
        Digenetic = two

    – Sperm-to sperm duct, copulatory
      apparatus, eversible cirrus
    Sexual repro flukes
   Female Structures
    – Ovary to oviduct to ootype
    – Oviduct joined by vitelline duct
    – Seminal receptacle = blind pouch off of
      oviduct
    – Single uterus sometimes modified as vagina
      near female gonopore
    Fluke reproduction
   Mutual cross-fertilization
   Sperm stored in seminal receptacle
   Eggs - oviduct to ootype then fertilized
   r-selected strategy (high fecundity)
   a – acetabulum
   d - vitelline ducts
   f - vitelline follicles
   o - oral sucker
   oe – oesophagus
   oo – ootype
   ov – ovary
   ph – pharynx
   sr - seminal receptable
   t – testis
   u - uterus
Fluke life-cycles
   Monogenetic
    – One host
    – Mostly external parasites of fish


   Digenetic
    – Two or more hosts
    – Mostly internal parasites
 Fluke life-cycles:
Chinese liver fluke
Fluke life-cycles

   Digenetic Fasciola = sheep liver fluke
    – Multiple hosts
    – Internal parasite of vertebrates
    – Intermediate host usually gastropod
Fluke life-cycles
Schistosoma mansoni
Schistosomiasis = disease with
 problems from egg production, fevers,
 eggs lodged in various tissues
Schistosomiasis
Schistosoma spp. cause
swimmer’s itch
 Exam I
Mean = 79

90-97   9
80-89   1
70-79   7
60-69   2
< 60    4
Class Cestoda

   Tapeworms
    – Internal parasite
    – Body with tegument
    – Body with anterior scolex, short neck and
      proglottids
    – No digestive system
Tapeworms = cestodes
   Locomotion
    – Sedentary: adult on host intestinal wall
    – Capable of muscular undulations

   Attachment
    – Scolex
    – Anterior with hooks or adhesive pad
Tapeworm digestion

   No mouth, no digestive tract

   Nutrients absorbed across tegument
Tapeworm Nervous System

   Cerebral ganglion; nerve ring in scolex
   Each proglottid has additional ganglia;
    connect to longitudinal nerve cords
   Sensory organs reduced, tactile receptors in
    scolex
Sexual Repro: tapeworms

   Hermaphroditic
   Mutual cross-fertilization
   Self-fertilization in some
Proglottids

 – Numerous testes along margins
 – Collecting tubules to coiled sperm duct
 – Vas deferens to genital pore
Proglottids
 – Two ovaries
 – Uterus = blind sac
     Tapeworm sex and fertilization
   Cirrus of each mate inserted into genital pores
   Sperm stored, eggs fertilized in oviduct
   Capsule material and yolk cells stored in uterus
   When mature, proglottids break free
Beef Tapeworm Life Cycle
Pork Tapeworm Life Cycle

								
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