Which one is absent in echinoderms

Options

A. Nervous system
B. Muscular System
C. Cephalisation
D. All the above.

Answer

To answer the question "Which one is absent in echinoderms?", we will analyze the options provided and determine which one is not present in echinoderms.

### Step-by-Step Solution:

1. **Understanding Echinoderms**:
- Echinoderms belong to the phylum Echinodermata, which is part of the kingdom Animalia. They include organisms such as starfish, sea urchins, and sea cucumbers.

2. **Examining the Organ Systems**:
- Echinoderms have an organ system level of organization, which means they possess various organ systems.

3. **Option 1: Nervous System**:
- Echinoderms do have a nervous system. However, it is decentralized and lacks a true brain. Instead, they have a nerve net and radial nerves.

4. **Option 2: Muscular System**:
- Echinoderms also possess a muscular system, which is important for their movement and feeding.

5. **Option 3: Cephalization**:
- Cephalization refers to the concentration of sensory and neural organs at one end of the body, typically forming a head with a brain. In echinoderms, cephalization is absent because they do not have a well-defined head or brain structure.

6. **Option 4: All of the Above**:
- Since both the nervous system and muscular system are present in echinoderms, this option is not correct.

7. **Conclusion**:
- The only option that is absent in echinoderms is **cephalization**. Therefore, the correct answer is **Option 3: Cephalization**.

### Final Answer:
**Cephalization is absent in echinoderms.**

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