Give general characters of platyhelminthes and their economic importance.

Explanation

General characters of phylum platyhelminthes are as follows:
(i) Body form of platyhelminthes is dorsoventrally flattened. It may be leaf like or ribbon like.
(ii) Flatworms have bilateral symmetry.
(iii) There is organ level of organisation in platyhelminthes.
(iv) Platyhelminthes are triploblastic animals with three germ layers-ectoderm, endoderm and mesoderm.
(v) Flatworms are acoelomates and true segmentation is absent.
(vi) A definite head appears first time in platyhelminthes. It remains forward during locomotion. The
head contains sensory organs.
(vii) Skeleton system and appendages are absent in platyhelminthes.
(viii) Digestive tract is incomplete in platyhelminthes.
( ix) Respiratory organ is absent. Respiration occurs through general body surface.
(x)In platyhelminthes, circulation occurs with the help of parenchymal fluid.
(xi) Excretion occurs through flame cells in platyhelminthes.
(xii) Asexual reproduction occurs through binary fission. Platyhelminthes are monoecious in nature. Fertilization is commonly internal in platyhelminthes.
Economical importance of platyhelminthes are as follows:
(i) Dugesia is used in regeneration experiments.
(ii) Fasciola hepatica damage the liver of host and causes liver - rot disease.
(iii) Tapeworm causes taeniasis in man while its cysticercus larva causes cysticercosis.