Homonomous metamerism is found in

Options

A. Arthropods
B. Annelids
C. Molluscs and vertebrates
D. All the above.

Answer

**Step-by-Step Solution:**

1. **Understanding Metamerism**: Metamerism refers to the segmentation of an organism's body into repeated units or segments. These segments can be both external and internal, and they work together to perform various functions in the organism.

2. **Types of Metamerism**: There are two main types of metamerism:
- **Homonymous Metamerism**: In this type, the segments are similar in structure and function, and both ectoderm and mesoderm contribute to the formation of these segments. This is also referred to as true metamerism.
- **Heteronymous Metamerism**: In this type, the segments are different from each other in structure and function, and typically only one layer (ectoderm) contributes to the segmentation.

3. **Identifying the Organisms**: Now, we need to analyze the given options:
- **Arthropods**: These organisms, such as cockroaches, exhibit pseudo-segmentation. Their segments are primarily formed from the ectoderm and are independent of one another, thus they do not show homonymous metamerism.
- **Annelids**: This group includes earthworms, which exhibit true or homonymous metamerism. Their body segments are both internally and externally segmented and work together in a coordinated manner.
- **Mollusks and Vertebrates**: Both of these groups show heteronymous metamerism, where their body segments are not true segments and do not function in a coordinated manner like those in annelids.

4. **Conclusion**: Based on the analysis, homonymous metamerism is found primarily in annelids, such as earthworms. Therefore, the correct answer to the question is **annelids**.

**Final Answer**: Homonymous metamerism is found in **annelids**.

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