In some chrodates, the notochord is modified as the vertebral column. Such animals are called vertebrates which one of the following statements make sense.

Options

A. All chordates are vertebrates but all vertebrates are not chordates
B. all vertebrates are chordates and all chordates are vertebrates
C. all vertebrates are chordates but all chordates are not vertebrates
D. chordates are not vertebrates and vertebrates are not chordates

Answer

To solve the question regarding the classification of chordates and vertebrates, we can break down the information step by step:

### Step 1: Understand the Definitions
- **Chordates**: This is a phylum that includes animals with a notochord, which is a flexible rod-like structure that provides support. All chordates also possess a nerve cord, pharyngeal gill slits, and a post-anal tail at some stage of their development.
- **Vertebrates**: These are a subphylum of chordates where the notochord is replaced or modified into a vertebral column (backbone).

### Step 2: Analyze the Options
We need to evaluate the four options given in the question:
1. All chordates are vertebrates, but all vertebrates are not chordates.
2. All vertebrates are chordates, and all chordates are vertebrates.
3. All vertebrates are chordates, but all chordates are not vertebrates.
4. Chordates are not vertebrates, and vertebrates are not chordates.

### Step 3: Evaluate Each Statement
- **Option 1**: Incorrect. All vertebrates are indeed chordates since they belong to the phylum Chordata.
- **Option 2**: Incorrect. While all vertebrates are chordates, not all chordates are vertebrates (e.g., tunicates and cephalochordates).
- **Option 3**: Correct. All vertebrates are chordates, but there are chordates (like tunicates and cephalochordates) that are not vertebrates.
- **Option 4**: Incorrect. This statement contradicts the definition since vertebrates are a subset of chordates.

### Step 4: Conclusion
Based on the analysis, the correct answer is **Option 3**: "All vertebrates are chordates, but all chordates are not vertebrates."