In hemichordates the dorsal nerve cord is

Options

A. Absent
B. Present throughout
C. Restricted to tongue region
D. Restricted to collar region

Answer

### Step-by-Step Solution:

1. **Understanding Hemichordates**: Hemichordates are a group of marine animals that exhibit some features similar to chordates, but they are not classified as true chordates. They have a body divided into three main regions: the proboscis, collar, and trunk.

2. **Identifying the Dorsal Nerve Cord**: In hemichordates, the dorsal nerve cord is a significant feature. It is important to determine where this nerve cord is located within the body structure of hemichordates.

3. **Analyzing the Options**:
- **Absent**: This option suggests that hemichordates do not have a dorsal nerve cord at all. This is incorrect, as hemichordates do possess a nerve cord.
- **Present Throughout**: This option implies that the nerve cord runs the entire length of the body. This is also incorrect, as the nerve cord is not present throughout the hemichordate body.
- **Restricted to Tongue Region**: This option suggests that the nerve cord is located only in the tongue region. This is incorrect because the nerve cord is not found in the tongue region.
- **Restricted to Collar Region**: This option indicates that the nerve cord is confined to the collar region of the body. This is the correct option, as in hemichordates, the dorsal nerve cord is indeed located in the collar region.

4. **Conclusion**: Based on the analysis of the options, the correct answer is that in hemichordates, the dorsal nerve cord is **restricted to the collar region**.