Open circulatory system is present in `:-`

Options

A. Annelids and Chordates
B. Annelids and Arthropods
C. Arthropods and Chordate
D. Arthropods and Mollusca

Answer

To answer the question regarding which organisms possess an open circulatory system, we can follow these steps:

### Step-by-Step Solution:

1. **Define Open Circulatory System**:
- An open circulatory system is characterized by the absence of blood vessels. In this system, blood (or hemolymph) is not confined to vessels but instead flows freely through cavities or sinuses.

2. **Identify Key Features**:
- In an open circulatory system, the heart pumps blood directly into open spaces or sinuses.
- These sinuses are areas where the blood bathes the organs directly, allowing for the exchange of nutrients and waste.

3. **Identify Organisms with Open Circulatory Systems**:
- Open circulatory systems are primarily found in certain groups of animals, notably:
- **Arthropods**: This group includes insects, arachnids, and crustaceans. For example, the cockroach is a common example of an arthropod with an open circulatory system.
- **Mollusks**: This group includes animals such as snails, clams, and octopuses. Mollusks typically have a shell, and the blood circulates in sinuses around the organs.

4. **Conclusion**:
- Therefore, the organisms that possess an open circulatory system are arthropods and mollusks.

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

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