Chondrichthyes have ................ tail fin, mouth on the............ side and do not have ................

Explanation

To answer the question regarding Chondrichthyes, we can break it down into three parts based on the provided information.

1. **Tail Fin**: Chondrichthyes have a **heterocercal** tail fin. This means that their tail fin has two lobes that are asymmetrical, with the vertebral column extending into the upper lobe, making it larger than the lower lobe. This structure is typical for species like sharks.

2. **Mouth Position**: The mouth of Chondrichthyes is located on the **ventral side**. This positioning allows them to capture prey from below, which is advantageous for their feeding habits.

3. **Absence of Structure**: Chondrichthyes do not have a **swim bladder**. Instead, they rely on constant swimming to maintain buoyancy. Without a swim bladder, if they stop swimming, they would sink.

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