Phylum Platyhelminthes has 3 classes -- Trematoda, Turbellaria and Cestoda
Class Cestoda :- It includes all tape worms. These are internal parasites
with a complex life history. The life cycle involves two hosts.
Their body characters are adaptations for parasitic life. Mouth and
alimentary canal are absent. Food is absorbed through general body surface.
The head is called the scolex. It has a ring of hooks for attach-
ment to the host tissue. The body consists of several segments called
Proglottids. (eg) sheep and cattle tape worms.
class Turbellaria -- they are aquatic, planaria shows regeneration.
class Trematoda --
These are flukes living as parasites inside a host . A protective cuticle covers the outer surface of the body. The examples are Fasciola
(liver fluke), Schistosoma (blood flu kes).