In Amphioxus, circulatory system is

Options

A. Closed
B. Without heart
C. Without repiratory pigment
D. All the above

Answer

**Step-by-Step Solution:**

1. **Identify the Organism**: The question refers to Amphioxus, which is also known as Branchiostoma. It belongs to the subphylum Cephalocordata within the phylum Chordata.

2. **Understand the Circulatory System Type**: Amphioxus has a closed circulatory system. This means that the blood circulates within blood vessels, as opposed to an open circulatory system where blood flows freely in body cavities.

3. **Heart Presence**: In Amphioxus, there is no heart. The blood vessels are contractile, meaning they can contract and relax to help move the blood. This eliminates the need for a separate pumping organ like a heart.

4. **Respiratory Pigment**: The blood of Amphioxus does not contain any respiratory pigments (like hemoglobin). Instead, it relies on the dissolved oxygen in the blood to meet its oxygen requirements for vital functions.

5. **Conclusion**: Since all the statements about the circulatory system of Amphioxus are correct (it is closed, without a heart, and without respiratory pigment), the correct answer is "all of the above."

**Final Answer**: All of the above.

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