Question

Acoelomate Phylum is

A. Nemathelminthes

B. Nematoda

C. Platyhelminthes

D. Both A & C

Answer 1

Hint: Animals which are classified under the Acoelomate Phylum lack coelom or a definite body cavity. Proper body cavity is found only in multicellular organisms with proper tissues. Acoelomate is the simplest example of Triploblastic organisms in that their body has three embryonic layers- the endoderm, the mesoderm and the ectoderm.

Complete answer:

Nemathelminths is a phylum consisting of the thread or round shaped horsehair worms. They are mostly parasitic. They are bilaterally symmetrical, triploblastic with an unsegmented body. Their body cavity is filled with muscles. They are a category of roundworms.

Nematoda is the other name for Nemathelminthes which are organisms with tough and resistant cuticles. They have a perivisceral cavity. However, their perivisceral cavity is more extensive than Platyhelminthes. They are pseudocoelomates, that is they can form a coelom when required. Examples for Nematoda are Ascaridida, Adenophorea and so on.

As we know that Platyhelminthes is Acoelomate Phylum, Nemathelminthes is not. So, option D is incorrect.

Platyhelminthes are thin, soft, leaf-like or ribbon-like organisms. They are triploblastic animals without a body cavity. Hence, we can say that Acoelomate Phylum is the other name for Platyhelminthes. 

So, the correct answer is Option (C).

Note:

Phylum Nematoda is a pseudocoelomate whereas Platyhelminthes are acoelomates. Hence, there is a clear differentiation between Nematoda and Platyhelminthes though they have many other similarities in the body structure. Apart from this, there is one other basic difference between Nemathelminths and Platyhelminthes, which is the former is roundworm and the latter is flatworm.