Protists having transverse and longitudinal groove in their theca are

Options

A. Foraminiferans
B. Radiolarians
C. Diatoms
D. Dinoflagellates.

Answer

To solve the question about which protists have transverse and longitudinal grooves in their theca, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for protists that have both transverse and longitudinal grooves in their theca. The term "theca" refers to a protective outer covering or shell that some protists possess.

2. **Identify the Options**: The options provided are:
- Option 1: Foraminiferans
- Option 2: Radiolarians
- Option 3: Diatoms
- Option 4: Dinoflagellates

3. **Analyze Each Option**:
- **Foraminiferans**: These are single-celled organisms with a shell made of calcium carbonate. They do not have transverse and longitudinal grooves in their theca.
- **Radiolarians**: These are also single-celled organisms with intricate silica-based skeletons. They do not possess theca with grooves.
- **Diatoms**: These are photosynthetic algae with a siliceous skeleton, but they do not have transverse and longitudinal grooves in their theca.
- **Dinoflagellates**: These protists have a unique structure with two flagella (one transverse and one longitudinal) and possess a theca that has grooves. The transverse flagellum is located in a groove called the cingulum, while the longitudinal flagellum trails behind.

4. **Conclusion**: Based on the analysis, the correct answer is **Option 4: Dinoflagellates**. They are characterized by having both transverse and longitudinal grooves in their theca.

### Final Answer:
The protists having transverse and longitudinal grooves in their theca are **Dinoflagellates**.

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