Question

There is no true internal body cavity or coelom in
A. Echinodermata
B. Vertebrata
C. Mollusca
D. Platyhelminthes

Answer 1

Hint: Coelom cavity is found in animals in which various organs are present. Organisms with true coelom are called coelomates while animals in which no true body cavity is present are called acoelomates. Cnidaria, Porifera, Ctenophora and Platyhelminthes are acoelomates. Echinodermata, Vertebrata and Mollusca are higher animals. They have a true coelom.

Complete answer:
Animals have mainly three types of body forms on the basis of which they are classified as: coelomates, acoelomates, and pseudocoelomates. True coelomates have fluid filled cavities that are completely present in the layer of tissue. Acoelomates lack this cavity. Pseudocoelomates have a fluid cavity that is not completely encased in a layer of tissue.
Platyhelminthes include worms that have a flat body. There is no coelom present in the body of Platyhelminthes that’s why they are known as acoelomates.
Echinodermata includes marine animals. They have bilateral symmetry and have true coelom. They come in the category of coelomates.
Vertebrates are the higher animals they have a fully developed body. They have vertebrae. They include fish, amphibians, reptiles, and mammals. They have true coelom.
Mollusca are evolved from free living flatworms. They have an internal body cavity enclosed by mesodermal membranes. Their coelom is reduced to a small space and is called Haemocoel.
From the above information we have found that Platyhelminthes have no internal body cavity or coelom.

So, the correct answer is option D.

Note: Platyhelminthes are parasitic in nature. They do not have respiratory and circulatory systems. It includes lung fluke, liver fluke, tapeworms etc. Echinodermata are very useful for humans as they are an important source of food and medicines. They also have many ecological benefits. Sand dollars and sea cucumbers burrow into the sand to provide more oxygen in the depths of the sea floor. They are also used in scientific research.