Pseudocoelom is found in …………. .

Explanation

**Step-by-Step Solution:**

1. **Understanding Pseudocoelom**: Pseudocoelom is a type of body cavity that is not entirely lined by mesoderm. It is referred to as a "false coelom" because it does not have the same structural integrity as a true coelom.

2. **Formation of Pseudocoelom**: In organisms with a pseudocoelom, the mesoderm does not completely surround the endoderm. Instead, there is a space between the mesoderm and the endoderm, which is filled with fluid. This body cavity is formed during the development of the organism.

3. **Identification of Organisms with Pseudocoelom**: Pseudocoelom is primarily found in organisms belonging to the phylum Nematoda, commonly known as roundworms. These organisms exhibit a pseudocoelom that serves various functions, including providing space for the internal organs and allowing for movement.

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