All Protochordates are :

Options

A. Freshwater
B. Marine
C. Aquatic
D. None of these

Answer

### Step-by-Step Solution:

1. **Understanding Protochordates**: Protochordates are a group of animals that include organisms that exhibit characteristics of both invertebrates and vertebrates. They are considered to be the evolutionary link between these two groups.

2. **Identifying the Group**: The question asks about the group in which protochordates are found. Protochordates are primarily classified under the subphylum "Protochordata," which includes hemichordates.

3. **Characteristics of Protochordates**: Protochordates possess a notochord, which is a flexible rod-like structure that provides support. However, they lack a true vertebral column (backbone) and have a nerve cord that is more similar to invertebrates.

4. **Habitat**: Protochordates are typically found in marine environments. They inhabit the sea and are often found in benthic zones (the lowest level of a body of water).

5. **Examples**: Some examples of protochordates include organisms like "Ascidians" (sea squirts) and "Herdmania," which are both marine animals.

6. **Conclusion**: Based on the characteristics and habitat of protochordates, we can conclude that they are primarily found in marine environments.

### Final Answer:
All protochordates are marine organisms.

---