Moneran phylogeny is best evidenced by sequence of nucleotides in RNA of ribosomes. On the basis of this information, the most primitive monerans are :-

Options

A. Archaebacteria
B. Eubacteria
C. Filamentour bacteria
D. Cyanobacteria

Answer

**Step-by-Step Solution:**

1. **Understanding Moneran Phylogeny**: The question asks about the phylogeny of Monerans, which refers to the evolutionary relationships among these organisms. The best evidence for this phylogeny comes from the nucleotide sequences in ribosomal RNA (rRNA).

2. **Identifying Moneran Groups**: The options provided are Archaebacteria, Eubacteria, Filamentous bacteria, and Cyanobacteria. We need to analyze which of these groups represents the most primitive form of Monerans.

3. **Characteristics of Archaebacteria**: The term "Archaebacteria" suggests that these organisms are ancient. They are single-celled prokaryotes that lack a nucleus and have distinct ribosomal RNA structures compared to other bacteria.

4. **Significance of rRNA**: The ribosomal RNA, particularly the 16S rRNA, is crucial for understanding the evolutionary relationships among organisms. The unique differences in the ribosomal RNA of Archaebacteria indicate that they diverged early in the evolutionary timeline.

5. **Extreme Environments**: Archaebacteria are known for their ability to thrive in extreme environments, such as highly acidic, salty, or hot conditions. This adaptability further supports their classification as some of the most primitive life forms.

6. **Conclusion**: Based on the evidence from ribosomal RNA sequences and the characteristics of Archaebacteria, we conclude that the most primitive Monerans are Archaebacteria.

**Final Answer**: Archaebacteria

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