Which one is the common ancestral larval from of echinoderms, hemichordates and chordates ?

Options

A. Tornaria
B. Bipinnaria
C. Dipleurula
D. Trochophore

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the common ancestral larval form of echinoderms, hemichordates, and chordates. This requires knowledge of the larval forms associated with these groups.

2. **Identifying the Options**: The options provided are:
- Tornaria
- Bipinaria
- Diplerula
- Trochophora

3. **Analyzing Each Option**:
- **Tornaria**: This larval form is specific to hemichordates. It does not represent a common ancestor for all three groups.
- **Bipinaria**: This larval form belongs to echinoderms. Like Tornaria, it does not represent a common ancestor for all three groups.
- **Trochophora**: This larval form is associated with mollusks and is not relevant to echinoderms or hemichordates.
- **Diplerula**: This larval form is known to be associated with echinoderms and is considered to be the common ancestral larval form for echinoderms, hemichordates, and chordates.

4. **Conclusion**: Based on the analysis, the common ancestral larval form of echinoderms, hemichordates, and chordates is **Diplerula**.

### Final Answer:
The common ancestral larval form of echinoderms, hemichordates, and chordates is **Diplerula**.

---