Phylum Platyhelminthes

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Phylum Platyhelminthes

Flatworms

Flukes Tapeworms

Monogenian

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Phylum PlatyhelminthesThe phylum consists of four classes

– Turbellaria (flatworm)– Trematoda (fluke)– Cestoda (tapeworm)– Monogenian

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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

Reproduction

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Nervous SystemFree-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, benthic, tiny and inconspicuous

– Primarily marine and freshwater, many interstitial

– 4,500 speciesFree-living

Flatworm

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Flatworm Body Plansbilateral symmetryAcoelomatetriploblastic

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Digestion Mouth is usually located at the anterior end or mid-body on

ventral surface 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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DigestionMouth is usually located at the

anterior end or mid-body on ventral surface

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Feeding 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

Feeding Habits

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Excretion

Excretory system – Contains

flame bulbs

Nervous SystemPosses several

nerve cords with a centralized ganglia (brain)

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ReproductionReproduction occurs

with the reciprocal exchange of sperm

Fertilized eggs are released and usually develop directly into flatworms– Muller's larva

• Chemosensory to find mate• Hermaphroditic

Mating & Reproduction

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Regeneration Many species posses remarkable powers of

regeneration and repair wounds

flatworm

nudibranch

Camouflage

• Staurosporine

• Tetrodoxin

HawaiianFlatworms

Class Turbellaria

Pseudoceros dimidiatus

Pseudoceros cf. rubroanus

Pseudoceros ferrugineus

Pseudobiceros sp.

Planocera cf. oligoglena

Class Turbellaria

Hawaiian Flatworms

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Class Cestoda (Tapeworms)

Defining characteristics– Scolex– Proglottids

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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