ABSTRACT
Platyhelminthes are unique for the presence of ectolecithality and neoblasts; the latter serve as a model for studies on cancer and senescence. Of 27,700 species, 77 % of them are vertebrate parasites and harmful to man and his food basket from livestock and fish. Motility rather than body size of the definitive (vertebrate) host (DH) has been the driving force in evolution and diversification in parasitic flatworms. Being relatively more fecund than the free-living turbellarians, the parasitic flatworms compensate the huge loss incurred during the transmission phases. Bereft of a mouth and gut, the cestodes are relegated to the host’s gut and abstract low molecular nutrients through the immune-resistant tegument. The turbellarian neoblasts undertake symmetric mitosis, whereas the germinal/germinative cells of digeneans and cestodes that lack vasa and piwi orthologs undergo asymmetric mitosis.
