Which is not a homiotherm?

Options

A. Aptenodytes
B. Testudo
C. Delphinus
D. Neophron

Answer

To determine which organism is not a homeotherm, we first need to understand the definitions of homeotherms and poikilotherms.

### Step-by-Step Solution:

1. **Define Homeotherms**: Homeotherms are animals that maintain a constant internal body temperature regardless of external environmental conditions. This group primarily includes mammals and birds.

2. **Define Poikilotherms**: Poikilotherms, on the other hand, are organisms that cannot regulate their internal body temperature and instead rely on external environmental temperatures. This group includes reptiles, amphibians, and fish.

3. **Identify the Organisms**: The question provides a list of organisms to evaluate:
- Aptenodytes (a genus of penguins, which are birds)
- Testudo (a genus of tortoises, which are reptiles)
- Delphinus (a genus of dolphins, which are mammals)
- Neophron (a genus of vultures, which are birds)

4. **Classify Each Organism**:
- **Aptenodytes**: As a bird, it is a homeotherm.
- **Testudo**: As a reptile, it is a poikilotherm.
- **Delphinus**: As a mammal, it is a homeotherm.
- **Neophron**: As a bird, it is a homeotherm.

5. **Determine the Answer**: Among the listed organisms, Testudo (the tortoise) is the only one that is not a homeotherm, as it is a poikilotherm.

### Final Answer:
**Testudo (tortoise) is not a homeotherm.**

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