Identify the phylum/phyla in which some animals show parasitism.

Options

A. Nematoda
B. Platyhelminths
C. Annelida
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Parasitism**: Parasitism is a relationship where one organism (the parasite) benefits at the expense of another organism (the host). The parasite derives nutrients from the host, which can lead to the host's illness or malnutrition.

2. **Identifying Relevant Phyla**:
- **Phylum Nematoda**: This phylum includes roundworms, many of which are parasitic. A notable example is *Ascaris*, which infects the human intestine and absorbs nutrients from the host.
- **Phylum Platyhelminthes**: This phylum includes flatworms, such as tapeworms and liver flukes, which are also parasitic. These organisms live in the digestive system of their hosts and extract nutrients, causing various diseases.
- **Phylum Annelida**: This phylum includes segmented worms. Some members, like leeches, are known to be parasitic as they feed on the blood of their hosts. Certain polychaetes can also absorb nutrients from their environment, which may include parasitic behavior.

3. **Conclusion**: Based on the examples provided, all three phyla—Nematoda, Platyhelminthes, and Annelida—contain animals that exhibit parasitism. Therefore, the correct answer is that all of these phyla show parasitism.

**Final Answer**: All of these (Nematoda, Platyhelminthes, Annelida).

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