Open blood vascular system without any respiratory pigment is found in

Options

A. Earthworm
B. Cockroach
C. Nereis
D. Hydra

Answer

To solve the question "Open blood vascular system without any respiratory pigment is found in," we will follow these steps:

### Step 1: Understand the Open Blood Vascular System
An open blood vascular system is characterized by blood not being confined exclusively to blood vessels. Instead, the blood (hemolymph) flows freely through cavities in the body, allowing direct contact with tissues. This system is typically found in certain invertebrates.

**Hint:** Look for organisms where blood is not contained in a closed system of vessels.

### Step 2: Identify the Role of Respiratory Pigments
Respiratory pigments, such as hemoglobin, are molecules that transport oxygen in the blood. The question specifies an organism that lacks these pigments, indicating a simpler respiratory mechanism, often through diffusion.

**Hint:** Consider organisms that do not require complex respiratory systems or pigments for gas exchange.

### Step 3: Analyze the Options
1. **Adform (Earthworm)**: Belongs to the phylum Annelida, which has a well-developed closed circulatory system. Therefore, this option is incorrect.

2. **Nares (another annelid)**: Similar to the earthworm, it also has a closed circulatory system. This option is incorrect as well.

3. **Hydra**: A simple organism that does not have a circulatory system. Gas exchange occurs through diffusion, but it does not have a blood vascular system. Thus, this option is also incorrect.

4. **Cockroach**: This organism has an open circulatory system where blood is not confined to vessels and is instead found in a body cavity known as hemocoel. Additionally, cockroaches do not have respiratory pigments like hemoglobin.

**Hint:** Focus on the organism that has an open circulatory system and lacks respiratory pigments.

### Step 4: Conclusion
After analyzing the options, the organism that has an open blood vascular system without any respiratory pigment is the **Cockroach**.

**Final Answer:** The correct answer is **Cockroach (Option 2)**.