Question

Arrange the larval developmental stages of pearl oyster in sequence
(A) Eyespot
(B) Veliger
(C) Pediveliger
(D) Trochophore larva
Choose the correct answer from the options given below:

• A. (D), (A), (B), (C)
• B. (B), (C), (D), (A)
• C. (D), (B), (A), (C)
• D. (B), (C), (A), (D)

Hint:

The trochophore is the earliest larval stage in marine bivalves, while the pediveliger (characterized by the foot, "pedi-") is the final stage before settlement.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Pearl oysters (*Pinctada* spp.) undergo indirect development with distinct planktonic larval stages before settling on a substrate as a sessile spat.

Step 2: Detailed Explanation:
After external fertilization, the embryonic development of the pearl oyster progresses through the following larval stages:
1. Trochophore larva (D): A free-swimming, ciliated stage that develops within 24 hours of fertilization.
2. Veliger larva (B): Developed from the trochophore, it possesses a larval shell (making it D-shaped) and a ciliated feeding organ called the velum.
3. Eyespot stage (A): A mature veliger stage where a distinctive, dark pigmented eyespot develops.
4. Pediveliger larva (C): The final larval stage, featuring a functional foot used to crawl on and select a suitable settlement substrate.
This is followed by metamorphosis into a sessile Spat.
Therefore, the correct chronological sequence is: (D) $\rightarrow$ (B) $\rightarrow$ (A) $\rightarrow$ (C).

Step 3: Final Answer:
The sequential arrangement corresponds to Option C.