All of the following are monoecious, except

Options

A. Fasciola
B. Spongilla
C. Ascaris
D. Ctenoplana

Explanation

To solve the question "All of the following are monoecious, except," we need to identify which organism among the options provided is dioecious (having separate male and female individuals) rather than monoecious (having both male and female reproductive organs in the same individual).

### Step-by-Step Solution:

1. **Understand the Terms:**
- **Monoecious:** Refers to organisms that have both male and female reproductive organs in the same individual. Examples include many plants and some animals like sponges and earthworms.
- **Dioecious:** Refers to organisms that have separate male and female individuals. Examples include many animals like humans and certain species of worms.

2. **Analyze the Options:**
- **Fasciola:** This is a genus of parasitic flatworms (flukes) that belong to the phylum Platyhelminthes. Fasciola is monoecious, meaning it has both male and female reproductive organs in the same organism.
- **Esponzilla:** This is a freshwater sponge from the phylum Porifera. Sponges are also monoecious, possessing both male and female reproductive structures.
- **Ascaris:** This is a genus of parasitic roundworms (nematodes). Ascaris is dioecious, meaning it has distinct male and female individuals. Males are typically smaller than females.
- **Tenoplana:** This organism belongs to the phylum Ctenophora and is also monoecious, having both male and female reproductive organs.

3. **Identify the Exception:**
- From the analysis, we can see that Fasciola, Esponzilla, and Tenoplana are all monoecious. The only organism that is dioecious is Ascaris.

4. **Conclusion:**
- Therefore, the answer to the question "All of the following are monoecious, except" is **Ascaris**.

### Final Answer:
Ascaris