Trochophore larva occurs in

Options

A. Annelida and porifera
B. Coelenterata annelida
C. Mollusca and Echinodermata
D. Annelida and Mollusca

Explanation

**Step-by-Step Solution:**

1. **Understanding Trochophore Larva:**
- Trochophore larvae are small, translucent, free-swimming larvae characterized by a spherical or pear-shaped body and a ring of cilia around them, known as the prototroch. This structure helps them swim in marine environments.

2. **Identifying Organisms with Trochophore Larvae:**
- Trochophore larvae are primarily found in certain groups of marine animals, specifically in:
- Annelida (segmented worms)
- Mollusca (such as gastropods and bivalves)

3. **Analyzing the Options:**
- **Option 1: Annelida and Porifera**
- Annelida has trochophore larvae, but Porifera (sponges) do not. Thus, this option is incorrect.
- **Option 2: Selenoprata and Annelida**
- Selenoprata is not a recognized group in this context, and while Annelida does have trochophore larvae, this option is not valid. Therefore, it is incorrect.
- **Option 3: Mollusca and Echinodermata**
- Mollusca has trochophore larvae, but Echinodermata (like starfish) do not. Hence, this option is also incorrect.
- **Option 4: Annelida and Mollusca**
- Both Annelida and Mollusca have trochophore larvae. This option is correct.

4. **Conclusion:**
- The correct answer is that trochophore larvae occur in **Annelida and Mollusca**.

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