Taxonomically the most controversal group is :-

Options

A. Dinoflagellates
B. Diatoms
C. Euglenoids
D. Prokaryote

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which group of organisms is the most controversial in terms of taxonomy. Taxonomy is the science of classification of living organisms.

2. **Analyzing the Options**: The options provided are:
- Dinoflagellates
- Diatoms
- Euglenoids
- Prokaryotes

3. **Evaluating Each Group**:
- **Dinoflagellates**: These are primarily marine plankton and are known for their unique characteristics, but they are generally well classified within the Protista kingdom.
- **Diatoms**: These are a group of microalgae with silica cell walls, and they are also well-defined taxonomically.
- **Prokaryotes**: This group includes bacteria and archaea, which are also well classified, although there can be some debate about certain classifications within this group.
- **Euglenoids**: This group is unique because they exhibit characteristics of both plants and animals. They have chloroplasts and can perform photosynthesis (similar to plants), but they lack a cell wall and can also exhibit heterotrophic behavior (similar to animals).

4. **Identifying the Controversy**: The euglenoids' dual characteristics create confusion in classification. They can be classified under both Plantae (due to their chloroplasts) and Animalia (due to their lack of a cell wall and heterotrophic nutrition). This ambiguity makes them the most controversial group taxonomically.

5. **Conclusion**: Based on the analysis, the most controversial group taxonomically is **Euglenoids**.

**Final Answer**: Euglenoids

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