Besides Annelida and Arthropoda, metamer-
ism is found in

Options

A. Cestoda
B. Mollusca
C. Chordata
D. Acanthocephala

Answer

### Step-by-Step Solution:

1. **Understanding Metamerism**: Metamerism refers to the division of an organism's body into repeated segments or metameres. This segmentation can be observed both internally and externally.

2. **Identifying Groups with Metamerism**: The question asks for groups besides Annelida (segmented worms) and Arthropoda (insects, arachnids, crustaceans). We need to identify other groups that exhibit metamerism.

3. **Analyzing the Given Options**: The options provided are:
- Sestoda (a class of flatworms)
- Mollusca (snails, clams, etc.)
- Chordata (vertebrates and some invertebrates)
- Acanthocephala (parasitic worms)

4. **Evaluating Each Option**:
- **Sestoda**: These are flatworms that do not exhibit true metamerism.
- **Mollusca**: Generally, mollusks do not show true metamerism, although some may have a body plan that appears segmented.
- **Chordata**: This group includes vertebrates, which do exhibit metamerism in the form of segmented bodies (e.g., vertebrae).
- **Acanthocephala**: These are parasitic worms that do not show metamerism.

5. **Conclusion**: Among the options, Chordata is the only group that exhibits true metamerism alongside Annelida and Arthropoda.

### Final Answer:
Besides Annelida and Arthropoda, metamerism is found in **Chordata**.

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