Which of the following has closed circulatory system ?

Options

A. Arthropoda
B. Annelida
C. Platyhelminthes
D. Mollusca

Answer

To determine which of the following options has a closed circulatory system, we will analyze each option provided:

1. **Arthropoda**:
- Arthropods, which include insects, arachnids, and crustaceans, have an open circulatory system. In this system, the blood (hemolymph) is not confined entirely within blood vessels and bathes the organs directly in a hemocoel.
- **Hint**: Remember that arthropods have a hemolymph that flows freely in body cavities.

2. **Annelida**:
- Annelids, such as earthworms, possess a closed circulatory system. In this system, the blood is contained within vessels, allowing for more efficient transport of nutrients and gases.
- **Hint**: Annelids are segmented worms with a more complex circulatory system compared to arthropods.

3. **Platyhelminthes**:
- Platyhelminthes, or flatworms, do not have a circulatory system at all. They rely on diffusion for the transport of nutrients and gases due to their flat shape.
- **Hint**: Flatworms are simple organisms that do not require a circulatory system because of their body structure.

4. **Mollusca**:
- Mollusks, such as snails and octopuses, typically have an open circulatory system, although some cephalopods (like octopuses) have a more complex system that can be considered closed. However, in general, mollusks are classified with an open system.
- **Hint**: Most mollusks have an open circulatory system, but some exceptions exist.

After analyzing all the options, we conclude that the only group with a closed circulatory system is **Annelida**.

**Final Answer**: The correct answer is **Option 2: Annelida**.