Which is not characteristic of all chordates ?

Options

A. Dorsal nerve cord
B. Diaphragm between thorax and abdomen
C. Coelom
D. Pharyngeal gill slits

Answer

To answer the question "Which is not characteristic of all chordates?", we need to identify the characteristics that are unique to certain groups within the phylum Chordata.

### Step-by-Step Solution:

1. **Understanding Chordates**:
- Chordates are a diverse group of animals that share certain key characteristics at some stage of their life cycle. The main characteristics include:
- A notochord (a flexible rod-like structure)
- A dorsal hollow nerve cord
- Pharyngeal gill slits
- A post-anal tail
- A coelom (body cavity)

2. **Identifying the Characteristics**:
- We need to evaluate the given options to see which characteristic is not found in all chordates.
- Common characteristics of all chordates include:
- Dorsal nerve cord
- Notochord
- Pharyngeal gill slits
- Coelom

3. **Analyzing the Options**:
- Among the options, we need to identify which one does not apply to all chordates.
- The diaphragm, which separates the thoracic cavity from the abdominal cavity, is a feature that is only present in vertebrates (a sub-group of chordates) and not in all chordates such as urochordates (like tunicates) and cephalochordates (like lancelets).

4. **Conclusion**:
- Therefore, the characteristic that is not found in all chordates is the diaphragm. This makes it the correct answer to the question.

### Final Answer:
The characteristic that is not found in all chordates is the diaphragm.

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