Phylum: Platyhelminthes - The Flatworms I Chapter 10 I F.Sc. I First Year I biology I Lec. 13

The common examples of flatworms are:
Dugesia (Planaria):
A free-living flatworms with a ciliated outer surface.
Fasciola (Liver fluke):
It is an endoparasite in sheep and occasionally in human beings. It has suckers used for
attachment to host tissue. It completes its life cycle in two hosts, a snail, sheep or
man. It lives in the bile duct of its hosts.
Taenia (Tape worm):
An endoparasite of humans, cattle and pig, which completes its life cycle in two hosts.
The intermediate host is pig or cattle.
Structure of body. The body is ribbon-like and divided into segments called
proglottids which contain mainly sex organs. The segments continue to break off and
are passed out from the intestine along with feces.
Adaptations for parasitic mode of life
The parasitic platyhelminthes have completely adapted themselves to parasitic mode of
life by the development of the following characteristics:
Cuticle. The epidermis is absent and there is the formation of resistant cuticle for
protection.
Adhesive organs. They have developed adhesive organs, such as suckers and
hooks, for attachment to the host.
Degenerated systems. There is degeneration of muscular system and nervous
system.
The digestive system has become simplified due to increased dependence on
host.
The reproductive systems are complicated and the ova are produced in huge
numbers to ensure continuity of the species.
Complexity in life cycle. The complexity of life cycle and presence of more
than one host during the life cycle is also an important parasitic adaptation.