Cephalization is absent in

Options

A. Molluscs
B. Arthopods
C. Both (1) and (2)
D. Echinoderms

Answer

**Step-by-Step Solution:**

1. **Understanding Cephalization**: Cephalization refers to the evolutionary development of a head, where sensory organs and nerve cells are concentrated at one end of the body. This is a significant feature in many animal groups.

2. **Identifying Groups of Animals**: To determine where cephalization is absent, we need to look at various animal groups. Common groups to consider include mollusks, arthropods, and echinoderms.

3. **Analyzing Mollusks**: Mollusks, such as snails and squids, exhibit a clear head region with sensory organs and a centralized nervous system. Therefore, they do have cephalization.

4. **Analyzing Arthropods**: Arthropods, including insects and crustaceans, also show distinct cephalization. They have a well-defined head with sensory organs and a complex nervous system.

5. **Analyzing Echinoderms**: Echinoderms, such as starfish and sea urchins, are unique in that they have a pentaradial symmetry and lack a distinct head region. They do not have concentrated neural ganglia or a sensory head, indicating that cephalization is absent in this group.

6. **Conclusion**: Based on the analysis, the group where cephalization is absent is the echinoderms.

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

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