In arthropodes which of the following is not true

Options

A. Circulatory system is of open type and are dioecious
B. Eyes are compound and simple both type
C. Fertilisation is external only
D. They are mostly oviparous with direct or indirect development

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which statement about arthropods is not true. We need to evaluate each statement provided to determine its validity.

2. **Evaluating the First Statement**:
- **Statement**: "The circulatory system is of open type and are dioshers."
- **Analysis**: Arthropods indeed have an open circulatory system where the heart pumps blood into the body cavity, allowing it to directly bathe the organs. "Dioshers" refers to dioecious organisms, meaning they have distinct male and female individuals. This statement is true.

3. **Evaluating the Second Statement**:
- **Statement**: "The eyes are compound and simple both types."
- **Analysis**: Arthropods possess both compound eyes (common in insects) and simple eyes (ocelli) found in various arthropods. This statement is also true.

4. **Evaluating the Third Statement**:
- **Statement**: "Fertilization is external only."
- **Analysis**: This statement is false because while many arthropods do have external fertilization, some, like cockroaches, have internal fertilization. Therefore, this statement is not true.

5. **Evaluating the Fourth Statement**:
- **Statement**: "They are mostly oviparous with direct or indirect development."
- **Analysis**: Most arthropods lay eggs (oviparous), and they can undergo direct development (where the young resemble the adult) or indirect development (involving larval stages). This statement is true.

6. **Conclusion**: The statement that is not true is "Fertilization is external only." This is the false statement among the options provided.

### Final Answer:
The statement that is not true about arthropods is: "Fertilization is external only."

---