Phylum Platyhelminthes

The "Flatworms"

  1. Unifying Characteristics
    1. Parasitic of free-living metazoan flatworms
    2. Bilaterally symmetrical
    3. Triploblastic, with well-developed organ system
    4. Excretory system generally of flame cells and ducts
    5. Nervous system includes a brain (cephalization)
    6. Acoelomate
    7. Generally hermaphroditic
  1. Platyhelminthes Classification

    1. Class Turbellaria
        1. Mostly free living, primarily aquatic and marine
        2. Bottom dwellers
        3. Mostly carnivorous
        4. Photoreceptive ocelli (primitive eyes)
        5. Auricles flanges on side of head
        6. Gut blind sac with two-way flow
        7. Examples Planaria
    1. Class Trematatoda (flukes)
          1. Entirely parasitic
          2. Body thickened into protective tegument
          3. Posses suckers
          4. Gut parasites
          5. Secrete enzyme interfering proteins
          6. Inactivate digestive enzymes
          7. Monogenetic and Digenetic Forms
    1. Monogenetic = single host
    2. ie: Polystoma of frog hosts

    3. Digenetic = two or more hosts

ie: Schistosoma, Clonorchis, Fasciola hepatica


    1. Class Cestoda (tapeworms)

          1. Entirely parasitic
          2. no digestive or nervous system
          3. live from digested materials
          4. body structures
          5. anterior scolex with suckers and barbs
          6. false segments called proglottids, each proglittid a self reproducing unit

                                          ie: Taenia pisiformis


    1. How to be a Good Parasite
          1. Reduction of sense of organs and nervous system
          2. Loss of locomotion organs
          3. Organs of adhesion developed
          4. Complicated life
          5. Tremendous egg production
          6. Protection from enzyme action, loss of cuticle
          7. Modified respiration, can survive anaerobic conditions.
          8. Loss of digestive tract; replaced with reproductive organs.


Name of Disease

Causative Organism


Definitive test

Snail Fever


Shistosoma mansoni

Freshwater Snail

Urine/Fecal Sample

Look for eggs

Shistosoma japonicum

Shistosoma haematobium

Beef Tapeworm

Taenia saginata


Stool Sample look for eggs (proglottids)

Pork Tapeworm

Taenia solium


Stool Sample look for eggs (proglottids)

Fish Tapeworm

Diphyllobothrium latum


Stool sample look for eggs (proglottids)