Which of the following is not a characteristic feature to all members of phylum Chordata?

Options

A. A notochord, a dorsal hollow nerve cord
B. A ventral heart
C. An endoskeleton
D. Vertebral column

Answer

To determine which of the following is not a characteristic feature of all members of the phylum Chordata, we need to analyze each option provided:

1. **Notochord**: This is a flexible rod-like structure that is present in all chordates at some stage of their development. It is a defining characteristic of the phylum Chordata.

2. **Dorsal hollow nerve cord**: This is another key feature of chordates. All members of this phylum possess a dorsal hollow nerve cord at some point in their life cycle.

3. **Endoskeleton**: While many chordates, particularly vertebrates, possess an endoskeleton, not all chordates have this feature. For example, some invertebrate chordates like tunicates do not have a true endoskeleton.

4. **Post-anal tail**: This is also a characteristic feature of all chordates during some stage of their development.

Now, let's summarize the findings:

- Options 1, 2, and 4 (notochord, dorsal hollow nerve cord, and post-anal tail) are present in all members of phylum Chordata.
- Option 3 (endoskeleton) is not present in all members of phylum Chordata, as some members like tunicates do not have an endoskeleton.

Therefore, the answer is **Option 3: an endoskeleton**.