Question

Explain.. true body cavity is absent in Platyhelminthes..

Answer 1

The organisms under phylum Platyhelminthes of Animalia are acoelomates -- meaning they don't have a true body cavity. This cavity in advanced animals surrounds the digestive tract; however since organisms under this phylum don't have complex digestive system they don't require a coelom. Hence they are also called flatworms. 

Answer 2

According to me the answer should be as follows:-

The organisms under phylum Platyhelminthes of Animalia are acoelomates -- meaning they don't have a true body cavity. This cavity in advanced animals surrounds the digestive tract; however since organisms under this phylum don't have complex digestive system they don't require a coelom. Hence they are also called flatworms.