Alimentary canal is not found in

Options

A. (a) Arachnida
B. (b) Apoda
C. (c) Gastropoda
D. (d) Cestoda

Answer

### Step-by-Step Solution:

1. **Understanding the Alimentary Canal**:
- The alimentary canal is a long tube that runs from the mouth to the anus and is part of the digestive system. It is responsible for the digestion and absorption of food.

2. **Analyzing the Options**:
- We need to determine which of the given options does not possess a well-defined alimentary canal.

3. **Option Analysis**:
- **Option A: Arachnida**:
- Arachnids, which include spiders and scorpions, have a well-defined digestive system and alimentary canal. Therefore, this option is not correct.

- **Option B: Amphibia**:
- Amphibians, such as frogs and salamanders, also possess a well-defined digestive system with an alimentary canal. This option is also not correct.

- **Option C: Gastropoda**:
- Gastropods, which include snails and slugs, have a complete digestive system with an alimentary canal. Thus, this option is not correct either.

- **Option D: Cestoda**:
- Cestodes, or tapeworms, belong to the phylum Platyhelminthes and are known for lacking a true alimentary canal. They absorb nutrients directly through their skin via specialized structures. Therefore, this is the correct answer.

4. **Conclusion**:
- The organism that does not have an alimentary canal is **Cestoda** (Option D).

### Final Answer:
**Cestoda**

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