All chordates posses

Options

A. Exoskeleton
B. Limbs
C. Skull
D. Axial skeletal rod of notochord

Answer

To solve the question "All chordates possess," we will analyze the options provided and determine which characteristic is universally found in all members of the phylum Chordata.

### Step 1: Understand the Phylum Chordata
Chordates are a diverse group of animals that share certain key characteristics. The phylum Chordata includes animals such as mammals, birds, reptiles, amphibians, and fish.

### Step 2: Identify Key Characteristics of Chordates
The defining features of chordates include:
1. **Notochord**: A flexible, rod-shaped structure that provides support.
2. **Dorsal Hollow Nerve Cord**: A nerve cord that runs along the back of the organism.
3. **Pharyngeal Gill Slits**: Openings in the throat region that may develop into gills in aquatic species.
4. **Post-anal Tail**: An extension of the body past the anal opening.
5. **Thyroid Gland**: A gland involved in metabolism.

### Step 3: Evaluate the Options
Now, let's evaluate the options given in the question:
1. **Exoskeleton**: Not all chordates possess an exoskeleton; many have an endoskeleton.
2. **Limbs**: Not all chordates have limbs; for example, fish do not have limbs.
3. **Skull**: While many chordates have a skull, some primitive chordates do not have a true skull.
4. **Axial Skeletal Rod of Notochord**: This is a characteristic that is present in all chordates during some stage of their development.

### Step 4: Conclusion
Based on the analysis, the correct answer is that all chordates possess the **axial skeletal rod of notochord**. This is a defining feature of the phylum Chordata, making option 4 the correct choice.

### Final Answer
**All chordates possess the axial skeletal rod of notochord (Option 4).**

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