In which one of the following group, brain box is absent :-

Options

A. Cyclostomata
B. Pisces
C. Amphibia
D. Urochordata

Answer

To solve the question "In which one of the following groups is the brain box absent?" we will analyze each of the given options step by step.

### Step-by-Step Solution:

1. **Understanding the Question**:
The question asks us to identify a group of animals that do not possess a "brain box," which refers to the presence of a well-defined brain.

2. **Analyzing Option 1: Cyclostoma**:
- Cyclostoma includes jawless fish such as lampreys and hagfish.
- These organisms do have a brain and a series of cranial nerves.
- **Conclusion**: Brain box is present in Cyclostoma.

3. **Analyzing Option 2: Pisces**:
- Pisces refers to fish in general, which include both jawless and bony fish.
- Fish have a well-developed brain and cranial nerves.
- **Conclusion**: Brain box is present in Pisces.

4. **Analyzing Option 3: Amphibia**:
- Amphibia includes frogs, toads, and salamanders.
- Amphibians have a brain, although it may be less developed compared to higher vertebrates.
- **Conclusion**: Brain box is present in Amphibia.

5. **Analyzing Option 4: Urochordata**:
- Urochordata, also known as tunicates, are marine animals that typically do not have a well-defined brain.
- They possess a simple nervous system and lack a true brain box.
- **Conclusion**: Brain box is absent in Urochordata.

6. **Final Answer**:
- Based on the analysis, the correct answer is **Option 4: Urochordata**, as this is the group where the brain box is absent.