Organ system level of organisation appeared for the first time in the members of 

Options

A. Platyhelminthes
B. Nematoda
C. Annelida
D. Arthropoda

Answer

To solve the question regarding which phylum first exhibited the organ system level of organization, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which phylum first displayed the organ system level of organization. This means we need to identify the phylum where organisms have a complex arrangement of organs working together.

2. **Define Organ System Level of Organization**: Organ systems are groups of organs that work together to perform complex functions. This level of organization is more advanced than just tissues or organs alone.

3. **Review the Options**: The options given are:
- A) Platyhelminthes (flatworms)
- B) Nematoda (roundworms)
- C) Annelida (segmented worms)
- D) Arthropoda (insects, arachnids, etc.)

4. **Analyze Each Phylum**:
- **Platyhelminthes**: These are flatworms and are known to have a more complex structure than simple organisms, but they do not have a true organ system level of organization.
- **Nematoda**: Roundworms have a tubular body structure and show some level of organization but are still not classified under the organ system level.
- **Annelida**: Segmented worms have a more developed organ system, including a circulatory system and digestive system.
- **Arthropoda**: This phylum includes insects and crustaceans, which have a highly developed organ system.

5. **Identify the Correct Answer**: Based on the analysis, the organ system level of organization first appeared in **Annelida**. However, the video transcript suggests that Platyhelminthes is the answer, which may indicate a misunderstanding. The correct answer based on biological classification is **Annelida**.

6. **Final Answer**: The organ system level of organization first appeared in the members of **Annelida**.