Which of the following has closed circulatory system ?

Options

A. Molluscs
B. Arthropods
C. Annelids
D. Platyhelminthes

Answer

To determine which of the following has a closed circulatory system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Closed Circulatory System**: A closed circulatory system is characterized by the presence of blood that circulates within closed vessels, known as blood vessels. This system allows for more efficient transport of nutrients and oxygen throughout the body.

2. **Analyze the Options**:
- **Mollusca**: This phylum includes various organisms. While some members, specifically cephalopods (like octopuses and squids), have a closed circulatory system, not all mollusks do. Therefore, this option cannot be considered correct as it refers to all mollusks.

- **Arthropoda**: Members of this phylum, such as insects and crustaceans, possess an open circulatory system. In this system, body fluids (hemolymph) bathe the organs directly, and there are no closed blood vessels. Thus, this option is incorrect.

- **Annelida**: This phylum includes segmented worms, which do have a closed circulatory system. Blood circulates within vessels, making this option correct.

- **Platyhelminthes**: This group includes flatworms, which do not have a circulatory system at all. Nutrients and gases are exchanged through diffusion. Therefore, this option is incorrect.

3. **Conclusion**: Based on the analysis, the correct answer is **Annelida**, as they are the only group listed that has a closed circulatory system.

### Final Answer:
The organism that has a closed circulatory system is **Annelida**.