Open circulatory system in present in

Options

A. Arthopods
B. Molluscs
C. Annelids
D. Both (1) & (2)

Answer

### Step-by-Step Solution:

1. **Understanding Open Circulatory System**:
- An open circulatory system is characterized by the absence of blood vessels that contain blood. Instead, blood (or hemolymph) flows freely within body cavities.

2. **Characteristics of Open Circulatory System**:
- In an open circulatory system, blood is not confined to vessels but rather bathes the organs directly in a hemocoel (a body cavity).
- This system allows for the direct exchange of nutrients and waste between blood and tissues.

3. **Identifying Organisms with Open Circulatory Systems**:
- Open circulatory systems are commonly found in certain groups of animals.
- **Arthropods**: This group includes insects, arachnids (like spiders), and crustaceans (like crabs and lobsters). They all possess an open circulatory system.
- **Mollusks**: This group includes snails, clams, and octopuses, which also have an open circulatory system.

4. **Exclusion of Other Groups**:
- **Annelids**: This group, which includes earthworms, has a closed circulatory system, where blood is contained within vessels.

5. **Conclusion**:
- Therefore, the open circulatory system is present in arthropods and mollusks.

### Final Answer:
The open circulatory system is present in **arthropods** and **mollusks**.

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