True segmentation ( metameric ) occurred for the first time in

Options

A. Platyhelminthes
B. Aschelminthes
C. Annelids
D. Arthropods

Answer

**Step-by-Step Solution:**

1. **Understanding True Segmentation**: True segmentation, also known as metamerism, refers to the division of the body into repetitive segments or metameres. This characteristic is significant in the classification of animals.

2. **Analyzing the Options**:
- **A. Platyhelminthes**: This phylum includes flatworms, which do not exhibit true segmentation. They have a simple body plan without distinct segments.
- **B. Aschelminthes**: This group includes roundworms and also lacks true segmentation. They may show some degree of body division, but it is not metameric.
- **C. Annelida**: This phylum includes segmented worms like earthworms and leeches. They exhibit true segmentation, where the body is divided into distinct segments that are internally and externally differentiated.
- **D. Arthropoda**: While arthropods do show segmentation, it is not considered true segmentation in the same way as in annelids. Their segmentation is more complex and involves specialized body regions.

3. **Conclusion**: Based on the analysis, true segmentation first occurred in the phylum **Annelida**. Therefore, the correct answer is **C. Annelida**.

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