Echinoderms are headless, brainless and heartless, Yet they are placed at the top of invertebrates because of presence of

Options

A. Enterocoel
B. Exclusive marine forms
C. High power of regeneration
D. Great power of reproduction.

Answer

### Step-by-Step Solution:

1. **Understanding Echinoderms**: Echinoderms are a group of marine animals that include starfish, sea urchins, and sea cucumbers. They are characterized by their radial symmetry and a unique water vascular system.

2. **Key Characteristics**: The question mentions that echinoderms are "headless, brainless, and heartless." This means they lack a centralized brain and heart, which are common features in many other animal groups.

3. **Importance of Body Cavity**: Despite lacking these features, echinoderms are considered to be at the top of the invertebrate classification. This is primarily due to the presence of a true coelom, specifically an enterocoel.

4. **Definition of Enterocoel**: An enterocoel is a type of body cavity that forms from the outpocketing of the embryonic gut (entron). This is different from a schizocoel, which forms through the splitting of mesoderm.

5. **Significance of Enterocoel**: The presence of an enterocoel is significant because it allows for more complex body structures and functions. It is a characteristic shared with more advanced groups like chordates.

6. **Comparison with Other Options**:
- **Exclusive Marine Forms**: While echinoderms are marine, this trait is not exclusive to them and does not explain their advanced status.
- **High Power of Regeneration**: While echinoderms can regenerate lost limbs, this ability is also found in other groups like cnidarians.
- **Great Power of Reproduction**: Many invertebrates, including arthropods, exhibit high reproductive rates, making this option less relevant.

7. **Conclusion**: The presence of an enterocoel is the defining feature that places echinoderms at the top of the invertebrate classification, despite their lack of a head, brain, and heart.

### Final Answer:
Echinoderms are placed at the top of invertebrates because of the presence of **enterocoel**.

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