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Phylum Platyhelminthes . Flatworms Flukes Tapeworms. Phylum Platyhelminthes. The phylum consists of four classes Turbellaria Trematoda Cestoda. Triclad Flatworm. Reproduction. Almost all are simultaneous hermaphrodites

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phylum platyhelminthes

Phylum Platyhelminthes




Phylum Platyhelminthes

phylum platyhelminthes2
Phylum Platyhelminthes
  • The phylum consists of four classes
    • Turbellaria
    • Trematoda
    • Cestoda

Triclad Flatworm

Phylum Platyhelminthes

  • Almost all are simultaneous hermaphrodites
  • Parasitic species (flukes and tapeworms) have complex lifecycles, with various hosts and several different larval stages
  • Incredible powers of regeneration

Phylum Platyhelminthes

nervous system
Nervous System
  • Free-living species usually have a well-developed sensory system
  • Parasites generally have less elaborate systems.


Phylum Platyhelminthes

taxonomic summary
Taxonomic Summary
  • Phylum Platyhelminthes (Flatworms)
    • Class Turbellaria
    • Class Cestoda
    • Class Trematoda
    • Class Monogeneans

Phylum Platyhelminthes

class turbellaria
Class Turbellaria
  • Most are free–living, tiny and inconspicuous
    • Primarily marine and freshwater



Phylum Platyhelminthes

flatworm body plans
Flatworm Body Plans
  • Exhibit bilateral symmetry, acoelomate, and are triploblastic
  • Parenchyma tissue

Phylum Platyhelminthes

digestion and excretion
Digestion and Excretion
  • Mouth is usually located at the anterior end or mid-body on ventral surface
  • Excretory system
    • Contains flame bulbs

Phylum Platyhelminthes

  • Many species posses remarkable powers of regeneration and repair wounds

Phylum Platyhelminthes

turbellarian lifestyles
Turbellarian Lifestyles
  • Most are benthic
  • Posses several nerve cords with a centralized ganglia (brain)

Phylum Platyhelminthes

turbellarian habits
Some species also have a protrusible pharynx that captures food and transfers it into the mouth

Can be carnivores or scavenge on dead animals and detritus

Turbellarian Habits

Phylum Platyhelminthes

  • Reproduction occurs with the reciprocal exchange of sperm
  • Fertilized eggs are released and usually develop directly into flatworms
    • Muller's larva

Phylum Platyhelminthes

class cestoda tapeworms
Defining characteristics



Class Cestoda (Tapeworms)

Phylum Platyhelminthes

  • Proglottids
    • Each animal can be 3,000 – 4,000 per animal
    • Amazing reproductive output
    • Each may contain several ovaries and 1,000 distinct testes

Phylum Platyhelminthes

beef tapeworm
Beef tapeworm

Phylum Platyhelminthes

problems of a parasitic existence
Problems of a parasitic existence
  • Reproduce within the definitive host
  • Get fertilized eggs out of the host
  • Contact a new and appropriate host
  • Obtain entrance into the host
  • Locate the appropriate environment within the host
  • Maintain position within the host
  • Withstand an often anaerobic environment
  • Avoid digestion or attack by the hosts immune system
  • Avoid killing the host, at least until reproduction is completed

Phylum Platyhelminthes

class trematoda flukes
Class Trematoda (Flukes)
  • All are external and internal parasites of other animals
  • Leech-like bodies with a sucker at each end
  • Have a gut and well-developed reproductive system, never segmented

Phylum Platyhelminthes

trematoda lifecycles
Trematoda Lifecycles
  • The lifecycle is complex with up to 4 different hosts and several larval types

Phylum Platyhelminthes

trematodes of concern

Deadly prominent disease in many regions of the world

Bores into the skin of the definitive host and travels in the circulatory system to the heart the lungs and the kidneys where it feeds and grows

Inflammation is caused by eggs becoming trapped in the hosts tissues

Chinese liver fluke

Lives in the bile duct of humans, cats, and dogs (1-2 cm.)

Goes through two intermediate hosts

Infection occurs from ingestion of raw fish

Trematodes of Concern

Phylum Platyhelminthes