Colonial urochordate is

Options

A. Ciona
B. Doliolum
C. Pyrosoma
D. Salpa

Answer

### Step-by-Step Solution:

1. **Understanding Colonial Urochordates**:
- Urochordates, also known as tunicates, are a subphylum under Phylum Chordata. They are characterized by having a notochord only during their larval stage; in adults, the notochord is absent.

2. **Identifying the Options**:
- The question provides four options:
1. Ciona
2. Doliolum
3. Pyrosoma
4. Salpa

3. **Analyzing Each Option**:
- **Ciona**: This is a solitary form of urochordate and does not form colonies.
- **Doliolum**: Also typically a solitary form and does not exhibit colonial behavior.
- **Salpa**: Similar to Ciona and Doliolum, Salpa is generally solitary.
- **Pyrosoma**: This is a colonial urochordate, known for forming free-floating colonies made up of many individuals called zoids.

4. **Conclusion**:
- Based on the analysis, the only colonial urochordate among the options provided is **Pyrosoma**. Thus, the correct answer is **Pyrosoma**.

### Final Answer:
**The colonial urochordate is Pyrosoma.**

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