Chordates with a backbone are called

Options

A. Protochordates
B. Agnatha
C. Gnathostomes
D. Vertebrates

Answer

**Step-by-Step Solution:**

1. **Understanding Chordates**: Chordates are a diverse group of animals that share certain key characteristics during some stage of their development. These characteristics include a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

2. **Identifying the Backbone**: In chordates, the notochord is a flexible rod-like structure that provides support. In many chordates, particularly in vertebrates, the notochord is replaced or modified into a backbone or vertebral column during development.

3. **Subphylum Classification**: Chordates are divided into different subphyla. The subphylum that includes animals with a backbone is called Vertebrata. This subphylum encompasses all vertebrates, which are characterized by having a vertebral column (backbone).

4. **Exclusion of Other Options**:
- Protochordates are not vertebrates and do not possess a backbone.
- Agnatha refers to jawless fish, which are part of the vertebrate group but do not represent the entire category of chordates with a backbone.
- Gnathostomes are jawed vertebrates, which also fall under the category of vertebrates.

5. **Conclusion**: Based on the classification and characteristics discussed, chordates with a backbone are specifically referred to as "Vertebrata."

**Final Answer**: Chordates with a backbone are called **Vertebrata**.

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