Long sized and tubular structures found in Gram-ve bacteria and helping in conjugation are called pili/fimbriae.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the long-sized tubular structures found in Gram-negative bacteria that aid in conjugation.

2. **Defining Conjugation**: Conjugation is a process where bacteria transfer genetic material to one another through direct contact. This is an important mechanism for genetic exchange and diversity among bacterial populations.

3. **Identifying the Structures**: In Gram-negative bacteria, the structures that facilitate this genetic transfer are known as pili (singular: pilus). These are long, tubular appendages that connect donor and recipient bacteria during the conjugation process.

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