Question

Study the following combinations:

Which of the above combinations are correct

• A. I and II
• B. I and III
• C. II and III
• D. III and IV

Hint:

Echinoderm larvae are bilaterally symmetrical, whereas adult echinoderms exhibit radial (pentamerous) symmetry.
This is a classic evolutionary example of retrogressive metamorphosis.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question requires us to evaluate four combinations of taxonomic classes, larval stages, and representative genera within the phylum Echinodermata, and select the correct combinations.

Step 2: Key Concepts and Approach:
Echinoderms exhibit indirect development with distinct, free-swimming bilateral larval stages.
We analyze the specific larval forms and representative genera for each of the five echinoderm classes to find the correct matches.

Step 3: Detailed Explanation:

• Combination I (Correct): Class Asteroidea (starfishes) has a free-swimming larva called Bipinnaria (and later Brachiolaria).
An example of this class is Pentaceros (sea pentagon).

• Combination II (Incorrect): While the larval stage of Class Crinoidea (sea lilies) is indeed Doliolaria, the genus Thyone belongs to the class Holothuroidea (sea cucumbers), not Crinoidea.

• Combination III (Correct): Class Holothuroidea (sea cucumbers) develops through a free-swimming Auricularia larval stage.
An example of this class is the genus Synapta.

• Combination IV (Incorrect): The larval stage of Class Echinoidea (sea urchins) is Echinopluteus.
However, the genus Neometra belongs to the class Crinoidea, not Echinoidea.


Step 4: Final Answer:
Only combinations I and III are correct, making option (B) the correct choice.