phylum platyhelminthes 1 flatworms flukes tapeworms
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Phylum Platyhelminthes2
Phylum Platyhelminthes
The phylum consists of four classes– Turbellaria – Trematoda– Cestoda
Triclad Flatworm
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Reproduction
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
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Nervous System
Free-living species usually have a well-developed sensory system
Parasites generally have less elaborate systems.
WHY?
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Taxonomic Summary
Phylum Platyhelminthes (Flatworms)– Class Turbellaria– Class Cestoda– Class Trematoda– Class Monogeneans
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Class Turbellaria
Most are free–living, tiny and inconspicuous – Primarily marine and
freshwater Free-living
Flatworm
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Flatworm Body Plans
Exhibit bilateral symmetry, acoelomate, and are triploblastic
Parenchyma tissue
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Digestion and Excretion
Mouth is usually located at the anterior end or mid-body on ventral surface
Excretory system – Contains flame
bulbs
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Regeneration
Many species posses remarkable powers of regeneration and repair wounds
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Turbellarian Lifestyles
Most are benthic
Posses several nerve cords with a centralized ganglia (brain)
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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
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Reproduction
Reproduction occurs with the reciprocal exchange of sperm
Fertilized eggs are released and usually develop directly into flatworms– Muller's larva
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Proglottids
Proglottids– Each animal can be
3,000 – 4,000 per animal
– Amazing reproductive output
– Each may contain several ovaries and 1,000 distinct testes
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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
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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
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Trematoda Lifecycles
The lifecycle is complex with up to 4 different hosts and several larval types
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Trematodes of Concern
Schistosomiasis – 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