Which is not found in vertebrates?

Options

A. Gill opening
B. Bilateral symmetry
C. Cnidoblasts
D. Body scales

Answer

To determine which option is not found in vertebrates, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Classification of Vertebrates**:
- Vertebrates belong to the subphylum Vertebrata, which is part of the phylum Chordata.
- They are divided into two main groups: Agnatha (jawless fishes) and Gnathostomata (jawed vertebrates).

2. **Identify the Types of Vertebrates**:
- Agnatha includes cyclostomes like lampreys and hagfish.
- Gnathostomata includes classes such as Chondrichthyes (cartilaginous fishes like sharks and rays) and Osteichthyes (bony fishes).
- Additionally, there are tetrapods, which include amphibians, reptiles, birds (Aves), and mammals.

3. **Review the Options Provided**:
- Analyze each option to see if it is associated with vertebrates.
- Look for features or structures that are typically found in vertebrates.

4. **Identify the Incorrect Option**:
- The term "nidoblast" refers to specialized cells found in organisms of the phylum Cnidaria (like jellyfish and hydra), which are not vertebrates.
- Therefore, nidoblasts are not found in vertebrates.

5. **Conclusion**:
- The correct answer is the option that mentions "nidoblast," as it is not associated with vertebrates.

### Final Answer:
The option that is not found in vertebrates is **nidoblast**.

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