2011Cestodes - 10/16/2011 Protozoa: Single Celled Organisms...

10/16/2011
1
• Protozoa
:
» Single Celled Organisms
» Eukaryotic
• Platyhelminthes - Flatworms
– Trematodes, Cestodes
-
• Nematodes
– Roundworms
• Arthropods
Cestodes
• Phylum Platyhelminthes (flatworms)
– Class Trematoda (flukes)
– Class Cestoidea (tapeworms)
Lack a mouth and
digestive tract.
– Subclass Eucestoda (true tapeworms)
– Order Pseudophyllidea
» Genus Diphyllobothrium
,
– Order Cyclophyllidea
» Genera: Taenia, Hymenolepis, Dipylidium

10/16/2011
2
General Characteristics
Morphology
• Multi-segmented and up to
25m long.
• Scolex - at anterior end
functions in attachment
• Neck - narrowest part of the
worm
• Strobila -made up of segments
of the worm called
proglottids .

10/16/2011
3
Scolex
• Acetabulate
- has four
suckers or muscular cups.
May have an armed
rostellum.
Bothriate -
two, four or
six longitudinally
arranged shallow
depressions

10/16/2011
4

10/16/2011
5
Tegument
• Lined with microvilli
– Glycocalyx
– Microthrices (microthrix)
• Nutrient absorption
• Tegumental and
parenchymal musculature –
circular and longitudinal
muscles
• Parenchyma-
space
enclosed by tegument
• Cestodes have a well developed nervous system .
A ‘brain’ in scolex is connected via nerves to the
strobila. Reproductive organs and musculature in
proglottids are extensively innervated.
• Osmoregulatory and excretory system- collecting
canals (ventral from scolex; dorsal to scolex)

10/16/2011
6
Reproductive System
• Proglottid has male and
female organs
• Proglottids on the same
worm or another worm
can engage in mating.
• Anapolytic worms
( Diphyllibothrium ) tanned
eggs exit through uterine
pore.
• Apolytic worms – entire
gravid proglottid is
released – no uterine pore
( Dipylidium)
Egg
• Egg is encased in a shell
• Layered
– outer envelope
– embryophore
– inner envelope
– oncosphere - embryo is
equipped with hooks and
will give rise to larval
form. Contain vitteline
cells as food source

10/16/2011
7
• Pseudophyllidean eggs are
tanned, have a ciliated
embryophore and have an
operculum at one end. From
within the oncosphere a
coracidium emerges (seen in
Diphyllobothrium latum ).
• Dipylidean eggs are thin shelled,
have a relatively thick outer
envelope and a non-ciliated
embryophore ( Dipylidium and
Hymenolepis ).
• Taenoid eggs lack shell and outer
envelope. Embryophore is
outermost covering ( Taenia and
Echinococcus ).
Life Cycle Patterns
Pseudophyllidean pattern
• Eggs released through uterine pore
are expelled in feces.
• Coracidia emerge and swim around
in water.