Section III. CLASS CESTODA
3-8.
GENERAL COMMENTS
This class consists of polyzoic (many body parts) flat worms commonly known as
tapeworms. Evolution has rendered these organisms as strict parasites incapable of a
free living condition. The digestive tract is absent and the worms absorb their nutrients
from the surroundings. The muscular system is poorly developed. The reproductive
system, on the other hand, has been developed to such an extent that over
90reproductive structures. Both male and female organs are found in each individual
segment which is called a proglottid. Excretion is handled by a pair of longitudinal
excretory canals which run the entire length of the proglottid. Longitudinal nerve cords
are also found to be shared by the complete worm. Reproduction is sexual and it is
performed internally. Most times, the tapeworms cross-fertilize between two different
worms, but fertilization may take place between two individual proglottids of the same
organism. They have a complex life cycle requiring, in most instances, at least one
intermediate host where the larval stages must develop prior to infecting the definitive
host again. Each individual life cycle will be discussed with the corresponding
organism.
3-9.
ORDERS
There are two orders within this class. The order Pseudophyllidea contains
Diphyllobothrium latum and Spirometra species. Cyclophyllidea contains members of
Taenia, Taeniarhynchus, Echinococcus, Hymenolepsis, and Dipylidium.
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