Pseudocoelom is present in

The correct option is C

Nematoda

The correct option is C:

Explanation of the correct option:

Option C:

1. The body cavity of nematodes is not lined by mesoderm.
2. Hence pseudocoelom is found in nematodes.
3. Pseudocoelom is a fluid-filled cavity lying inside the external body wall of an organism.
4. It is also known as false coelom, where the cavity is not lined by mesoderm.

Explanation for incorrect option(s):

Option A:

1. Annelida has a true coelom where the body cavity is lined by mesoderm.
2. It consists of all three layers: ectoderm, endoderm, and mesoderm.
3. It does not have pseudocoelom.

Option B:

1. Platyhelminthes are acoelomates.
2. They do not have a coelom.

Option D:

In protozoa, the coelom is absent.

Final answer: Pseudocoelom is present in Nematoda.