PHYLUM PLATYHELMINTHES

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PHYLUM PLATYHELMINTHES

• FLAT BODIED WORMS
• Class Turbellaria (planarians)
• mostly predatory
• free living
• Class Trematoda (internal flukes)
• only parasitic
• complex life-cycles
• Class Cestoda (tapeworms)
• only parasitic

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EXAMPLES

• PLANARIA FREE LIVING AQUATIC AND TERRESTRIAL
• Herbivore, carnivore, scavenger
• TAPEWORMS INTESTINAL PARASITE W/ MORE THAN 1
  HOST TAENIA
• FLUKES INTERNAL PARASITE W/MORE THAN ONE HOST
• BLOOD FLUKE SCHISTOSOMA
• LIVER FLUKE FASCIOLA

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TRAITS

• ORGAN LEVEL OF ORGANIZATION
• BILATERAL SYMMETRY
• SAC TYPE BODY 1 OPENING/ no anus
• GASTROVASCULAR CAVITY IS BRANCHED
• TRIPLOBLASTIC 3 GERM/tissue LAYERS
• CEPHALIZATION has a head
• BRAIN WITH 2 NERVE CORDS TRANSVERSE NERVES
• SENSE ORGANS light and chemicals
• Occeli/eyespots and auricles/ears

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TRAITS

• ACOELOMATE no coelom/body cavity
• DIFFUSION METHODS FOR
• GAS EXCHANGE - O2 and CO2
• WASTE REMOVAL by FLAME CELLS
• CIRCULATION of nutrients and waste
• REMEMBER DIFFUSION IS A SLOW PROCESS
  HI TO LO

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Epidermis/ ECTODERM
gut cavity
Lining of gut ENDODERM
no body cavity region between gut and body wall
packed with organs within MESODERM tissue
Acoelomate organism (flatworm)
Body Plan
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TRAITS

• MUSCLES FOR LOCOMOTION
• REPRODUCTION
• ASEXUAL REGENERATE
• SEXUAL HERMAPHRODITES BUT CROSS FERTILIZE

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EVOLUTIONARY MILESTONE

• ORGAN LEVEL OF ORGANIZATION
• reproductive, excretory, muscular
• BILATERAL SYMMETRY
• CEPHALIZATION
• Anterior and posterior
• Dorsal and ventral

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Platyhelminthes Taxonomy

• Classes of Phylum Platyhelminthes

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• --Widely distributed in N. America
• -- about 200 species
• --Occur in both lakes and streams
• -- Stream-dwelling species more differentiated
  than lake species
• --Species diversity increases in temperate areas
  20 to 60 species per lake

Planaria Class Turbellaria
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• Class Turbellaria
• Free-living flatworms mostly marine
• microscopic to two feet

• Locomotion in Turbellaria
• move by means of cilia and mucous
• 2 layers of muscle longitudinal and circular
• Stimulated by nervous system
• contractions for turning, twisting and folding
  of the body

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• Nutrition in Turbellaria
• carnivores and predators of other animals or dead
  remains.
• muscular pharynx is inserted into prey
• Secretes digestive enzymes
• Fragments are pumped into mouth on ventral
  surface
• Further digestion in gastrovascular cavity
• branching increases the surface area for
  digestion and absorption
• No anus, only mouth
• Undigested food excreted from mouth and pharynx
  as in cnidaria
• GVC aids both digestion and circulation
  distributes nutrients and oxygen to tissues

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Sensory/nervous

• Exhibits cephalization
• Group of nerve tissue (GANGLIA) at anterior
• Ganglia attached to 2 nerve chords
• well developed sensory eyespots for light
• auricles for chemical and mechanical (touch)
  receptors

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• Reproduction in Turbellaria
• Asexual---
• By fission or dividing
• Regeneration of missing parts
• Sexual-
• hermaphrodites w/ cross-fertilization
• Internal fertilization
• Zygote released to water

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EXCRETION IN TURBELLARIA
Excretory System
pharynx (protruded)
protonephridia
flame cell
nucleus
cilia

• Cilia of flame cells remove excess water and
  nitrogen wastes of body
• Waste moves to tubules
• Exits out pores in head
• Needs excretory system as tissues become thicker
  and more cells present

fluid filters through membrane folds
opening of tubule at body surface
flame cell
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Class Trematoda the Flukes
COMMON EXAMPLE OF COMPLEX LIFE CYCLE
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• Class Trematoda
• live as parasites
• protected from digestion by protein coat
• 2 suckers
• 1. Oral sucker attaches to organs of the host
  
• 2. Ventral sucker or acetabulum attaches to host
  tissues

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• Types of Hosts
• Complex life cycles
• Alternate between sexual and asexual stages
• Most require at least 2 different kinds of hosts
  to complete their life cycle
• 1. Definitive host (primary host)
• where parasite matures and reproduces (sexually)
• host in which eggs are released
• 2. Intermediate host
• Hosts in which larval stages develop and undergo
  asexual reproduction
• Results in an increase in the number of the
  individuals

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• Schistosoma
• a common blood fluke of SE Asia
• causes shistosomiasis
• Definitive host humans
• Intermediate host snails
• In humans - eggs penetrate and damage intestinal
  and bladder tissue
• constant inflammation and eventual deterioration
  of liver, spleen and other organs

Fluke Life Cycle
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• General Life Cycle - Chinese liver fluke,
  Clonorchis sinensis
• Adults live in the bile ducts of humans, dogs,
  and cats
• There are 2 intermediate hosts a snail and a
  fish
• Eggs are passed out of the definitive host and
  hatch as ciliated larvae called miracidia
• The miracidia penetrates a snail molluscan host
  and becomes a sporocyst
• They undergo asexual reproduction producing
  larvae called rediae
• Rediae often asexually produce more rediae, but
  will eventually give rise to larvae called
  cercariae
• They leave the molluscan host and penetrate fish
  
• They encyst in the fish tissues as the
  metacercaria
• Consumption of infected fish results in the
  metacercaria excysting in the gut and migrating
  to the bile duct

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• Class Cestoda
• Protective protein coat
• anterior region is called a scolex
• often armed with suckers and hooks

• Extending from neck of scolex is a series of
  proglottids
• contain sex organs and eggs
• no digestive system
• Mature eggs released through an opening in the
  proglottid
• leave the host when the proglottids break off

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b A definitive host eats infected, undercooked
beef
a Larvae become encysted in intermediate host
tissues
c Scolex of larva attaches to intestines wall
d Many proglottids form by budding
f Cattle may ingest embryonated eggs or ripe
proglottids to become intermediate hosts
e Ripe proglottids containing fertilized eggs
leave host in feces
Tapeworm Lifecycle
Class Cestoda
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• Beef Tapeworm, Taeniarhynchus saginatus
• Definitive host humans
• intermediate host cattle
• Eggs are shed with human feces
• infected persons defecate in a pasture or
  untreated sewage
• eggs are ingested by cattle
• Eggs hatch
• larvae bore into intestinal wall
• get into the circulatory system
• transported to muscle
• If uncooked beef is consumed the larvae is freed
  
• scolex develops, forming the adult
• Symptoms include loss of weight, chronic
  indigestion, diarrhea

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