Of the following statements which are not relevant to archaebacteria
They live in some of the most horsh habitats ,They are present in the gut of several ruminant animals
they are characterised by the presence of a rigid cell wall , They include mycoplasma
They are also referred to as blue- green algae.

Options

A. a , b and c
B. a , c and e
C. c , d and e
D. a c and d

Answer

To determine which statements are not relevant to archaebacteria, we will analyze each statement one by one:

1. **They live in some of the most harsh habitats.**
- This statement is relevant to archaebacteria. Archaebacteria are known for their ability to survive in extreme environments, such as hot springs, salt lakes, and acidic environments.

2. **They are present in the gut of several ruminant animals.**
- This statement is also relevant. Certain archaebacteria, specifically methanogens, are found in the digestive systems of ruminant animals, where they help in the digestion process.

3. **They are characterized by the presence of a rigid cell wall.**
- This statement is **not relevant** to archaebacteria. While archaebacteria do have cell walls, they are not rigid like those of bacteria. Instead, their cell walls are made of unique compounds, such as pseudopeptidoglycan, which differ from the peptidoglycan found in true bacteria.

4. **They include mycoplasma.**
- This statement is **not relevant** to archaebacteria. Mycoplasmas are a group of bacteria that lack a cell wall and are classified separately from archaebacteria.

5. **They are also referred to as blue-green algae.**
- This statement is **not relevant** to archaebacteria. Blue-green algae are actually cyanobacteria, which are a different group of organisms entirely.

Based on this analysis, the statements that are not relevant to archaebacteria are:
- They are characterized by the presence of a rigid cell wall.
- They include mycoplasma.
- They are also referred to as blue-green algae.

### Final Answer:
The statements that are not relevant to archaebacteria are:
- They are characterized by the presence of a rigid cell wall.
- They include mycoplasma.
- They are also referred to as blue-green algae.