Endocrine glands for the first time seen in

Options

A. Arthropoda
B. Nemathelminthes
C. Platyhelminthes
D. Porifera

Answer

**Step-by-Step Solution:**

1. **Understanding Endocrine Glands**: Endocrine glands are specialized glands that secrete hormones directly into the bloodstream. These hormones play crucial roles in regulating various bodily functions, including metabolism, growth, and reproduction.

2. **Identifying the First Appearance**: The question asks where the first endocrine glands were observed. To answer this, we need to look into the evolutionary history of animals and identify which group first exhibited these glands.

3. **Examining Invertebrate Groups**: We need to consider various invertebrate groups to determine where endocrine glands first appeared. The groups mentioned include:
- Arthropoda
- Nemathelminthes
- Platyhelminthes
- Porifera

4. **Analyzing Each Group**:
- **Arthropoda**: This group is known to have neurohormones secreted from endocrine glands. They are the first invertebrates where endocrine glands were observed.
- **Nemathelminthes**: This group does not have endocrine glands; instead, they possess a supraesophageal ganglion for message transfer.
- **Platyhelminthes**: This group is relatively simple and lacks any endocrine glands.
- **Porifera**: As one of the simplest animal groups, Porifera also does not have endocrine glands.

5. **Conclusion**: Based on the analysis, the first endocrine glands were seen in the group Arthropoda. Therefore, the correct answer is Arthropoda.

**Final Answer**: The first endocrine glands were seen in Arthropoda.

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