In which group of organisms the cell walls form two thin overlapping shells which fit together

Options

A. Slime moulds
B. Chrysophytes
C. Euglenoids
D. Dinoflagellates

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about a group of organisms whose cell walls form two thin overlapping shells that fit together. This description suggests a specific structural characteristic of the cell wall.

2. **Identifying the Organism Group**: The group of organisms that fits this description is the **chrysophytes**. This group includes diatoms, which are known for their unique cell wall structure.

3. **Describing the Cell Wall Structure**: In diatoms, the cell wall is made up of two parts:
- **Epitheca**: The upper part of the shell.
- **Hypotheca**: The lower part of the shell.
These two parts fit together like a soap box, which is a key characteristic of diatoms.

4. **Material Composition**: The cell wall of diatoms is primarily composed of silica, which is embedded in a cellulosic matrix. This silica gives the cell wall its rigidity and unique structure.

5. **Eliminating Other Options**:
- **Slime Molds**: They do not have a cell wall and exist in a plasmodial form, thus do not fit the description.
- **Euglena**: They have a flexible pellicle, not overlapping shells.
- **Dinoflagellates**: They have stiff cellulosic plates but do not form overlapping shells like those of diatoms.

6. **Conclusion**: Based on the analysis, the correct answer to the question is **chrysophytes**, specifically referring to the diatoms.

### Final Answer:
The group of organisms in which the cell walls form two thin overlapping shells that fit together is the **chrysophytes**.

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