What characteristics distinguish arthropods from annelids and molluscs ?

Explanation

To distinguish arthropods from annelids and molluscs, we can focus on several key characteristics, particularly the circulatory system, body structure, and other features. Here’s a step-by-step breakdown:

### Step 1: Circulatory System
- **Arthropods**: They possess an open circulatory system. This means that their blood (hemolymph) is not confined to vessels but instead flows freely through cavities (hemocoel) and bathes the organs directly.
- **Annelids**: They have a closed circulatory system, where blood is contained within vessels. This allows for more efficient transport of nutrients and gases.
- **Molluscs**: Most molluscs also have a closed circulatory system (with some exceptions like certain bivalves), similar to annelids.

### Step 2: Body Segmentation
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