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In the course of evolution, the true coe...

In the course of evolution, the true coelom
appeared first in

A

aschelminthes

B

annelide

C

arthropoda

D

echinodermata

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The correct Answer is:
**Step-by-Step Solution:** 1. **Understanding Coelom**: The term "coelom" refers to a body cavity that is completely lined by mesoderm. This is important in the classification of animals based on their body structure. 2. **Identifying True Coelom**: A "true coelom" is a body cavity that is fully surrounded by mesodermal tissue. This distinguishes it from a pseudocoelom, which is only partially lined by mesoderm. 3. **Analyzing the Options**: - **Option A: Acoelomates**: These organisms do not have a coelom. They are classified as acoelomates, which means they lack a body cavity entirely. Thus, this option is incorrect. - **Option B: Annelids**: Annelids are segmented worms that possess a true coelom. They are considered true coelomates and are the first group in which true coelom is observed. - **Option C: Arthropods**: While arthropods do have a coelom, they are not the first to exhibit a true coelom. They are considered coelomates, but the true coelom was not first seen in this group. - **Option D: Echinoderms**: Echinoderms also possess a true coelom, but they are not the first group in which it appeared. 4. **Conclusion**: Based on the analysis, the first appearance of a true coelom in the course of evolution is found in **Annelids**. **Final Answer**: Annelids ---
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