A cephalopod with an external shell is

Options

A. Sepia
B. Nautilus
C. Loligo
D. Octopus

Answer

To solve the question "A cephalopod with an external shell is," we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Cephalopods**: The question provides four options: Sepia, Nautilus, Loligo, and Octopus. We need to determine which of these cephalopods has an external shell.

2. **Understand Cephalopod Characteristics**: Cephalopods are a class of mollusks that typically have a soft body and are known for their intelligence and complex behaviors. Most cephalopods, like octopuses and squids, do not have an external shell.

3. **Examine Each Option**:
- **Sepia**: Commonly known as cuttlefish, they have an internal shell (cuttlebone) but no external shell.
- **Nautilus**: This is a cephalopod that possesses a prominent external shell, which is coiled and chambered.
- **Loligo**: This refers to squids, which also do not have an external shell; they have a reduced internal shell.
- **Octopus**: Octopuses are known for their lack of any shell, external or internal.

4. **Conclusion**: Based on the characteristics of each option, the only cephalopod that has an external shell is **Nautilus**.

5. **Final Answer**: Therefore, the correct answer to the question is **Nautilus**.