Which class shows 8 dorsal plates of shell?

Options

A. Amphineura
B. Monoplacophora
C. Scaphopoda
D. Cephalpoda

Answer

To determine which class of mollusks shows 8 dorsal plates of shell, we can analyze the options provided:

1. **Amphineura**: This class is known for having 8 overlapping dorsal plates. They are commonly referred to as sea cradle or chitons. Amphineura is characterized by its marine habitat, ranging from shallow waters to deep oceans. The presence of 8 dorsal plates is a distinctive feature of this class.

2. **Monoplacophora**: This class is incorrect for the question as they are primitive mollusks that typically possess a single, cap-like dorsal shell rather than 8 plates.

3. **Scaphopoda**: This class is also incorrect. Scaphopods have a tubular shell that is open at both ends, and they do not possess 8 dorsal plates.

4. **Cephalopoda**: This class includes animals like cuttlefish and octopuses. They have an internal shell or a reduced shell structure, not 8 dorsal plates.

Based on this analysis, the correct answer is **Amphineura**, as it is the only class that exhibits the characteristic of having 8 dorsal plates.

### Step-by-Step Solution:
1. **Identify the classes of mollusks provided**: Amphineura, Monoplacophora, Scaphopoda, and Cephalopoda.
2. **Analyze the characteristics of each class**:
- **Amphineura**: 8 overlapping dorsal plates.
- **Monoplacophora**: Single dorsal plate.
- **Scaphopoda**: Tubular shell open at both ends.
- **Cephalopoda**: Internal or reduced shell.
3. **Determine which class has 8 dorsal plates**: Only Amphineura fits this description.
4. **Conclude that the correct answer is Amphineura**.