Phylum Platyhelminthes includes triploblastic, acoelomate, bilaterally symmetrical and dorsoventrally compressed flatworms. Phylum Platyhelminthes has following characteristic features:
(1) Free-living, commensal or parasitic forms. They are heterotrophic in nature.
(2) Body cavity (coelom) lacking.
(3) Soft-bodied, unsegmented worms.