Bilateral, segmented bodies and hardened exoskeletons occur among the :

Options

A. arthropods
B. snails and clams
C. sponges
D. sea stars

Explanation

To solve the question regarding which group of animals exhibits bilateral symmetry, segmented bodies, and hardened exoskeletons, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Key Terms**:
- **Bilateral Symmetry**: This means the body can be divided into two identical halves along one plane.
- **Segmented Bodies**: This refers to bodies that are divided into sections or segments.
- **Hardened Exoskeletons**: This indicates a tough outer structure that protects the body, typically made of chitin or other materials.

2. **Identify the Animal Groups**:
- We need to consider various animal groups and see which one fits the description. Common groups include arthropods, annelids, mollusks, and echinoderms.

3. **Evaluate Arthropods**:
- Arthropods are known for their bilateral symmetry, segmented bodies, and a hardened exoskeleton. The exoskeleton is primarily made of chitin and can be reinforced with calcium carbonate in some species.

4. **Compare with Other Groups**:
- **Annelids**: They have segmented bodies and bilateral symmetry but lack a hardened exoskeleton.
- **Mollusks**: They have bilateral symmetry and some have shells, but they do not have segmented bodies in the same way arthropods do.
- **Echinoderms**: They exhibit radial symmetry and do not have a hardened exoskeleton in the same sense as arthropods.

5. **Conclusion**:
- Based on the characteristics analyzed, arthropods are the only group that possesses all three features: bilateral symmetry, segmented bodies, and hardened exoskeletons.

### Final Answer:
The correct answer is **arthropods**.