Which one of the following groups of animal reproduces only by sexual means?

Options

A. Ctenophora
B. Cnidaria
C. Porifera
D. Protozoa

Explanation

To determine which group of animals reproduces only by sexual means, we can analyze the options provided:

### Step 1: Analyze the first option - Tenophora
- Tenophora, also known as comb jellies, primarily reproduce sexually. They have both male and female reproductive organs, allowing for sexual reproduction. Therefore, Tenophora can reproduce only by sexual means.

### Step 2: Analyze the second option - Cnidaria
- Cnidaria includes organisms like jellyfish, corals, and sea anemones. They exhibit both sexual and asexual reproduction. The polyp form typically reproduces asexually, while the medusa form reproduces sexually. Thus, Cnidaria does not reproduce only by sexual means.

### Step 3: Analyze the third option - Porifera
- Porifera, or sponges, primarily reproduce asexually through processes such as fragmentation and budding. Some sponges can also reproduce sexually, but they do not exclusively reproduce by sexual means. Therefore, this option is incorrect.

### Step 4: Analyze the fourth option - Protozoa
- Protozoa are unicellular organisms and are classified under the protist kingdom, not the animal kingdom. They typically reproduce asexually through methods like binary fission. Therefore, this option is also incorrect.

### Conclusion
After analyzing all the options, the only group that reproduces exclusively by sexual means is **Tenophora**.

### Final Answer
The correct answer is **Tenophora**.

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