A true coelom is absent in phylum or Which of the following is pseudocoelomate

Options

A. Nematoda
B. Annelida
C. Echinodermata
D. Mollusca

Explanation

To answer the question regarding which phylum lacks a true coelom and which is pseudocoelomate, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Understanding Coelom**:
- A coelom is a fluid-filled body cavity that is completely lined by mesoderm. It provides space for the organs to grow and move independently of the body wall.
- There are three types of body plans based on the presence or absence of a coelom: acoelomate, pseudocoelomate, and coelomate.

2. **Types of Body Plans**:
- **Acoelomate**: Organisms that lack a coelom. The body is filled with mesenchyme (solid tissue).
- **Pseudocoelomate**: Organisms that have a pseudocoelom, which is a body cavity not completely lined by mesoderm. The cavity is derived from the blastocoel.
- **Coelomate (True Coelomate)**: Organisms that possess a true coelom, which is fully lined by mesoderm and allows for the development of complex organs.

3. **Identifying Pseudocoelomate Phylum**:
- The phylum that is classified as pseudocoelomate is **Nematoda** (roundworms). In nematodes, the body cavity is located between the endoderm and the mesoderm, making it a pseudocoelom.

4. **Conclusion**:
- The phylum that lacks a true coelom is **Nematoda**, which is pseudocoelomate.

### Final Answer:
The phylum that is pseudocoelomate is **Nematoda**.

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