Which one of the following protists is known as 'whirling whips' because of the spin produced by two flagella beating in opposing grooves along their hard surfaced bodies ?

Options

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

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about a specific type of protist known for its unique movement, described as "whirling whips."

2. **Identifying Key Terms**: The term "whirling whips" suggests a characteristic movement pattern. The question also mentions "two flagella" and "hard-surfaced bodies," which are important features to consider.

3. **Analyzing the Options**: The options provided are:
- A) Dinoflagellates
- B) Diatoms
- C) Euglenoids
- D) Heliosoids

4. **Recalling Definitions**:
- **Dinoflagellates**: These are protists that have two flagella and are known for their spinning movement. They often have a hard surface due to cellulose.
- **Diatoms**: These are algae with silica-based cell walls, not known for spinning.
- **Euglenoids**: These are flagellated protists, but they do not have the same spinning movement as dinoflagellates.
- **Heliosoids**: These are less commonly known and do not fit the description.

5. **Connecting Features to the Right Option**: The description of "two flagella beating in opposing grooves" aligns perfectly with the characteristics of dinoflagellates. Their movement is indeed described as "whirling" due to this unique structure.

6. **Conclusion**: Based on the analysis, the correct answer to the question is **A) Dinoflagellates**.

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