Which one is absent in Branchiostoma

Options

A. Head
B. Gill slits
C. Notochord
D. Dorsal hollow nerve cord

Answer

**Step-by-Step Solution:**

1. **Identify the Organism**: The question asks about Branchiostoma, which is also known as Amphioxus. It belongs to the subphylum Cephalochordata within the phylum Chordata.

2. **Understand the Characteristics of Branchiostoma**: Amphioxus is characterized by its pointed body at both ends and the presence of a notochord that extends throughout its life. It is often referred to as a lancelet due to its shape.

3. **Analyze the Structures in Question**: We need to determine which structure is absent in Branchiostoma. The options typically include:
- A) Head
- B) Gill Slits
- C) Notochord
- D) Dorsal Hollow Nerve Cord

4. **Evaluate Each Option**:
- **Head**: Branchiostoma does not have a distinguishing head. The body is elongated and lacks a well-defined head structure.
- **Gill Slits**: Branchiostoma has multiple gill slits that are used for respiration and feeding.
- **Notochord**: The notochord is a defining characteristic of all chordates, including Branchiostoma, and is present throughout its life.
- **Dorsal Hollow Nerve Cord**: This structure is also present in Branchiostoma, as it is a key feature of chordates.

5. **Conclusion**: Based on the analysis, the structure that is absent in Branchiostoma is the **head**.

**Final Answer**: The head is absent in Branchiostoma.

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