Which of the following is not a character uniting all chordates?

Options

A. Notochord
B. Spinal column
C. Dorsal, hollow nerve tube
D. Pharyngeal slits

Answer

To determine which of the following is not a character uniting all chordates, we need to first review the defining characteristics of chordates. The main features that unite all chordates include:

1. **Notochord**: A flexible rod-like 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 pharynx that can develop into gills in aquatic species.
4. **Post-anal Tail**: An extension of the body that is located behind the anus.

Now, let's analyze the options provided:

1. **Notochord**: This is a characteristic of all chordates.
2. **Spinal Column**: This is not a characteristic of all chordates. It is found specifically in vertebrates, which are a subgroup of chordates. Therefore, it does not unite all chordates.
3. **Dorsal Hollow Nerve Cord**: This is a characteristic of all chordates.
4. **Pharyngeal Gill Slits**: This is also a characteristic of all chordates.

Based on this analysis, the correct answer is the **Spinal Column**, as it is not a feature that unites all chordates but is specific to vertebrates.

**Final Answer**: The Spinal Column is not a character uniting all chordates.