What set of characters belongs to the same phylum?

Options

A. First true coelomates and nephridia as the excretory structures.
B. Pseudocoelomates and flame cells as the excretory structures
C. Acoelomates and metanephridia cells as the excretory structures
D. Eucoelomates and flame cells as the excretory structures.

Answer

To determine which set of characters belongs to the same phylum, we need to analyze each option based on the characteristics of the organisms involved.

### Step-by-Step Solution:

1. **Identify the First Option**:
- **Characters**: First true coelomates and nephredia as the excretory structures.
- **Analysis**: The first true coelomates are organisms from the phylum **Annelida** (e.g., earthworms and leeches). Nephredia are indeed the excretory structures found in these organisms.
- **Conclusion**: This option is correct.

2. **Identify the Second Option**:
- **Characters**: Pseudocoelomates and flame cells as the excretory structures.
- **Analysis**: Flame cells are excretory structures found in the phylum **Platyhelminthes** (flatworms). Pseudocoelomates refer to organisms with a pseudocoelom, which is not characteristic of Platyhelminthes, as they are acoelomates (no body cavity).
- **Conclusion**: This option is incorrect.

3. **Identify the Third Option**:
- **Characters**: Acoelomates and metanephridia as the excretory structures.
- **Analysis**: Metanephridia are excretory structures found in the phylum **Annelida** and also in some **Arthropoda**. Acoelomates do not have a body cavity, which is not consistent with metanephridia.
- **Conclusion**: This option is incorrect.

4. **Identify the Fourth Option**:
- **Characters**: Eucelomates and flame cells as the excretory structures.
- **Analysis**: Flame cells are found in **Platyhelminthes**, which are acoelomates. Eucelomates have a true coelom, which does not match with the characteristics of Platyhelminthes.
- **Conclusion**: This option is incorrect.

### Final Answer:
The set of characters that belong to the same phylum is **first true coelomates and nephredia as the excretory structures** (from the phylum Annelida).

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