Features such as dorso-ventrally flattened body, great power of regeneration and mostly endoparasitic animals belongs to the phylum:

Options

A. Mollusca
B. Arthropods
C. Platyhelminthes
D. Annelida

Answer

To solve the question about which phylum exhibits features such as a dorso-ventrally flattened body, great power of regeneration, and is mostly composed of endoparasitic animals, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Features**: The question mentions three specific features:
- Dorso-ventrally flattened body
- Great power of regeneration
- Mostly endoparasitic animals

2. **Analyze the Options**: The options provided are:
- Phylum Mollusca
- Phylum Arthropoda
- Phylum Platyhelminthus
- Phylum Annelida

3. **Evaluate Each Option**:
- **Phylum Mollusca**: This phylum includes animals like snails and octopuses, which do not have a dorso-ventrally flattened body and are not primarily endoparasitic.
- **Phylum Arthropoda**: This phylum includes insects and crustaceans, which also do not exhibit a dorso-ventrally flattened body or significant regeneration capabilities.
- **Phylum Platyhelminthus**: This phylum includes flatworms, which are characterized by their dorso-ventrally flattened bodies. They are known for their high regenerative abilities and many species are endoparasitic (like tapeworms).
- **Phylum Annelida**: This phylum includes segmented worms like earthworms, which do not have a dorso-ventrally flattened body and are not primarily endoparasitic.

4. **Conclude the Correct Answer**: Based on the analysis, the only phylum that matches all the given features is **Phylum Platyhelminthus**. Therefore, the correct answer is **C, Phylum Platyhelminthus**.

### Summary of the Solution:
The phylum that exhibits a dorso-ventrally flattened body, has great regenerative abilities, and consists mostly of endoparasitic animals is **Phylum Platyhelminthus**.