Which one of the following is not a characteristic feature of all the chordates?

Options

A. Presence of coelom
B. A diaphragm separeting thorax from abdomen
C. Dorsal nerve cord
D. Pharyngeal gill slits in the early embryonic stages

Answer

To determine which characteristic is not found in all chordates, we need to review the defining features of the phylum Chordata. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Key Features of Chordates
Chordates are defined by four main characteristics that must be present at some stage of their life cycle:
1. **Hollow Dorsal Nerve Cord**: This is a nerve cord located along the back of the organism.
2. **Notochord**: A flexible rod-like structure that provides support.
3. **Pharyngeal Slits**: Openings in the pharynx that may develop into gills in aquatic species.
4. **Post-anal Tail**: An extension of the body that follows the anal opening.

### Step 2: Analyze the Options
Now, we will evaluate the options provided in the question to see which one does not apply to all chordates:

1. **Presence of Coelom**: All chordates possess a coelom, which is a body cavity.
2. **Diaphragm Separating Thorax from Abdomen**: This feature is specific to mammals and is not found in all chordates.
3. **Dorsal Nerve Cord**: This is a characteristic of all chordates.
4. **Pharyngeal Gill Slits**: These are also present in all chordates during some stage of their development.

### Step 3: Conclusion
From the analysis, the feature that is not characteristic of all chordates is the **diaphragm separating thorax from abdomen**, as it is only found in mammals.

### Final Answer
The characteristic feature that is not found in all chordates is **the diaphragm separating thorax from abdomen** (Option 2).

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