Which of the following is not found in the phylum Chordata?

Options

A. A dorsal hollow nerve chord
B. Lateral paired gill slits during development
C. Anotochord at some stage of development
D. An external skeleton

Answer

To determine which option is not found in the phylum Chordata, we need to review the key characteristics of this phylum. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understand the Key Characteristics of Chordata**:
- Chordates are defined by four main characteristics at some stage of their development:
- Dorsal hollow nerve cord
- Notochord
- Pharyngeal (gill) slits
- Post-anal tail

2. **Analyze the Options**:
- We need to evaluate each option provided in the question to see if it aligns with the characteristics of Chordata.

3. **Identify the Characteristics**:
- **Dorsal Hollow Nerve Cord**: Present in all chordates.
- **Notochord**: Present at some stage of development in all chordates.
- **Gill Slits**: Present during the embryonic stage in many chordates.
- **Post-Anal Tail**: Present in all chordates at some stage.

4. **Identify the Incorrect Option**:
- The question asks for the characteristic that is **not** found in Chordata.
- The option that mentions an **external skeleton** does not fit because chordates typically have an **internal skeleton** made of bones or cartilage.

5. **Conclusion**:
- Therefore, the characteristic that is not found in the phylum Chordata is the **external skeleton**.

### Final Answer:
The characteristic that is not found in the phylum Chordata is the **external skeleton**.

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