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
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
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
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
Epidermis/
ECTODERM
gut cavity
Lining of gut
=ENDODERM
Acoelomate organism
(flatworm)
no body cavity; region between
gut and body wall packed with
organs within MESODERM
tissue
TRAITS
• MUSCLES FOR LOCOMOTION
• REPRODUCTION
– ASEXUAL – REGENERATE
– SEXUAL – HERMAPHRODITES BUT
CROSS FERTILIZE
EVOLUTIONARY
MILESTONE
• ORGAN LEVEL OF ORGANIZATION
– reproductive, excretory, muscular
• BILATERAL SYMMETRY
• CEPHALIZATION
– Anterior and posterior
– Dorsal and ventral
Platyhelminthes Taxonomy
Classes of Phylum Platyhelminthes
•
•
•
•
--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
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
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
Sensory/nervous
Brain/ganglia
•
•
•
•
•
nerve cords
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
Reproduction in Turbellaria
Asexual--•By fission or dividing
•Regeneration of missing parts
Sexual•hermaphrodites w/ cross-fertilization
•Internal fertilization
•Zygote released to water
testis
ovary
penis genital pore
oviduct
EXCRETION IN TURBELLARIA
Excretory pore
pharynx (protruded)
protonephridia
Flame cells
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
opening of
tubule at
body surface
flame cell
fluid
filters
through
membrane
folds
Excretory tubules
Class Trematoda – the Flukes
COMMON EXAMPLE
OF COMPLEX
LIFE CYCLE
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
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
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
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
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
b A definitive host eats
infected, undercooked beef
a Larvae
become
encysted in
intermediate
host tissues
c Scolex of larva
attaches to
intestine’s 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
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