Which of the following phyla contains members that are notorious for causing serious diseases in humans?

Options

A. Cnidarians
B. Segmented worms
C. Flatworms
D. Chordates

Explanation

To determine which phyla contains members that are notorious for causing serious diseases in humans, we can follow these steps:

### Step 1: Identify the Phyla
First, we need to identify the phyla that are known for containing organisms that can cause diseases in humans. Common phyla to consider include:
- Flatworms (Platyhelminthes)
- Roundworms (Nematoda)
- Arthropods (like mosquitoes and ticks)
- Protozoa (like Plasmodium)

### Step 2: Understand the Nature of the Organisms
Next, we need to understand the nature of the organisms within these phyla:
- **Flatworms (Platyhelminthes)**: Many flatworms are parasitic, such as tapeworms and liver flukes, which can cause serious diseases in humans.
- **Roundworms (Nematoda)**: Some roundworms, like hookworms and Ascaris, are also known to cause diseases.
- **Arthropods**: While not directly causing diseases themselves, they can be vectors for diseases (e.g., mosquitoes transmit malaria).
- **Protozoa**: Many protozoans are pathogenic and can cause diseases (e.g., malaria).

### Step 3: Analyze the Options
Given the options, we focus on the phyla that are primarily known for their parasitic nature:
- Flatworms (Platyhelminthes) are notorious for causing diseases like schistosomiasis and tapeworm infections.
- Roundworms (Nematoda) also cause diseases but are not the only phyla known for serious diseases.

### Step 4: Conclusion
Based on the analysis, the phylum that is most notorious for causing serious diseases in humans is **Flatworms (Platyhelminthes)**.

### Final Answer
The correct answer is **Flatworms (Platyhelminthes)**.

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