Question

In the life history and development of sea star, numerous larval forms are formed. Arrange them in the order of their occurrence:
A. Dipleurula
B. Branchiolaria
C. Bipinnaria
Choose the most appropriate answer from the options given below:

• A. A, B, C
• B. A, C, B
• C. B, A, C
• D. C, B, A

Hint:

Remember the alphabetical order trick for the main sea star larvae: \textbf{B}ipinnaria comes before \textbf{Br}achiolaria. The dipleurula is the conceptual starting form for all echinoderm larvae. So, Dipleurula \(\rightarrow\) Bipinnaria \(\rightarrow\) Brachiolaria.

Answer 1

The Correct Option is B

Step 1: Concept Overview:
Sea star (Asteroidea) development is indirect, featuring free-swimming, bilaterally symmetrical larval stages that precede metamorphosis into a radially symmetrical adult.

Step 2: Detailed Stage Descriptions:
1. Dipleurula (A): Considered the hypothetical echinoderm ancestor larva. It's the initial sea star larval stage, emerging from the gastrula and evolving into the bipinnaria. Essentially, the starting larval form.
2. Bipinnaria (C): The first distinct sea star larval stage. Developing from the dipleurula, it has a bilaterally symmetrical body with ciliated bands for movement and feeding, lacking attachment arms.
3. Brachiolaria (B): Formed from the bipinnaria larva and representing the final larval stage. Key features include three short, non-ciliated brachiolar arms and an adhesive disc at the anterior end. These are used for attachment before metamorphosis.

Step 3: Conclusion:
The correct larval development sequence is Dipleurula (early larva) \(\rightarrow\) Bipinnaria \(\rightarrow\) Brachiolaria, corresponding to A, C, B. Thus, option (B) is the answer.