Platyhelminthes

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Platyhelminthes

• Acoelomate Flatworms

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Todays Objective

• TSW take notes on the phylum Platyhelminthes
  including economic importance, an overview of
  class characteristics, and ecological niches.

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General Flatworm Characteristics

• Acoelomate no body cavity coelom- solid
  mesenchyme (mesoderm)
• First phylum to show a definite cellular mesoderm
• Bilaterally symmetrical
• Triploblastic 3 distinct tissue or germ layers
• Dorsoventrally flattened

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General Characteristics (cont.)

• Respiration by diffusion
• Digestive system extensively branched
• One opening for feeding and waste removal
• Lack an anus
• Primitive kidneys protonephridia with FLAME
  CELLS

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General Charcterisitcs (cont.)

• First evidence of cephalization primitive brain
• Some have eyespots
• Directional movement
• No true respiratory system or circulatory system
• Usually hermaphroditic

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Class Turbellaria

• Free-living flatworms
• Some freshwater (Planaria), marine, or
  terrestrial
• Most move by circular and longitudinal muscles
• Some move by using cilia (or cilia mucus)

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Turbellarian Feeding - Carnivorous

• Wrap body around prey
• Entangling with mucous
• Ingest the whole prey or suck its juices through
  a hardened stylet (modified pharynx)
• in many species the pharynx is completely
  eversible and can envelope the entire prey
• there is no anus so ingestion and egestion are
  through the mouth

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Turbellarian Reproduction

• Sexual Reproduction
• Most hermaphroditic
• Both sex organs discharge gametes into a common
  chamber even though this is true- cross
  fertilization is the most common mode of
  reproduction
• Some self fertilization can and does occur
• Asexual Reproduction
• Fragmentation and Regeneration

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Dugesia
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Class Monogenea

• Parasitic
• Flukes
• Only one host
• Most external parasites
• Gyrodactylus
• Polystoma
• Can cause major economic losses to fisheries

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Class Trematoda

• Digenetic Flukes
• Complex life history, involves 2 or more hosts
• Live in every type of environment
• 5,000 known species
• Live mostly in digestive system or associated
  organs (all parasitic)

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Some Trematodes of Importance

• Clonorchis Chinese human liver fluke
• Fasciola hepatica Liver fluke
• Schistosoma Blood fluke
• Know this life cycle!
• Where they are present it is hazardous to bathe,
  drink, wade in or dip your arms in infested
  waters!

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Class Cestoda - Tapeworms

• Long, Flattened
• White or Yellow in color
• All parasitic!
• Adults almost always live in the intestines of
  their hosts
• Body has protective cuticle
• Head (scolex) has multiple disks of hooks for
  attachment

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Cestodes (cont.)

• Can reach up to 50 ft. in length!
• No specialized sense organs
• Reproduce using proglottids (segments)
• Contain flame cells, nerves, muscles, male and
  female reproductive organs
• Shed in feces of host
• Taenia saginata beef tapeworm
• Taenia solium pork tapeworm

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Tapeworm Structure