Consider the following structures. (A) Notochord(B) Pharyngeal gill slits (C) Dorsal hollow nerve cord (D) Tail. How many structure are present in adult cephalochordate?

Options

A. Only (A)
B. Only (A) & (B)
C. (A), (B) & (C) only
D. (A), (B), (C) & (D)

Answer

To determine how many structures are present in adult cephalochordates from the given options, we will analyze each structure mentioned in the question:

1. **Notochord (A)**:
- Cephalochordates, such as lancelets, possess a notochord throughout their life. This structure provides support and is a characteristic feature of all chordates.

2. **Pharyngeal gill slits (B)**:
- Adult cephalochordates also retain pharyngeal gill slits. These structures are involved in filter feeding and respiration.

3. **Dorsal hollow nerve cord (C)**:
- The dorsal hollow nerve cord is another key feature of cephalochordates that persists into adulthood. It is part of the central nervous system.

4. **Tail (D)**:
- Adult cephalochordates have a post-anal tail, which is a characteristic of chordates. This tail is used for locomotion.

Now, compiling the information:
- All four structures (A, B, C, and D) are present in adult cephalochordates.

Thus, the answer to the question is that all four structures are present in adult cephalochordates.

**Final Answer**: Option D (A, B, C, D) - All four structures are present in adult cephalochordates.