Question

A pearl oyster belongs to class of
a. Mollusca
b. Bivalvia
c. Scaphopoda
d. Gastropoda

Answer 1

Hint: Pearl is a white highly shining globular in shape structure which is also called as the moti and these are formed by the oysters within its shell. Pearl is formed as a result of nacreous secretion from the mantle around a sand particle or a foreign particle.

Complete answer:
- Oysters are sedentary, marine bivalves that are found in all seas, except in the colder ones. The indian Pearl oyster is Pinctada vulgaris that is known for yielding precious pearls.
- The two shells are unequal, with the left one comparatively larger than right.
- Oysters remain attached to a rock. The adductor muscle is single and large. The foot is lacking in the adult.

On the basis of the structure of foot , respiratory organs, mantle and shell, molluscs are divided into six classes:
> Monoplacophora: It includes marine animals having segmentation only in a few organs. Their body is bilaterally symmetrical and triploblastic. They have five pairs of gills and six pairs of nephridia. It possesses the characters of Mollusca as well as Annelida.

> Amphineura: It includes marine organisms with flattened body and ventral. large and flat muscular foot.

> Scaphopoda: It includes marine organisms having tubular shells that are open at both ends. Their feet are conical and divided into lobes. They do not have gills and are dioecious.

> Gastropoda: It includes animals with twisted and asymmetrical bodies due to torsion. They have a well developed head with eyes and tentacles. Their shell is univalve and spirally coiled. Their feet are also large and flat.

> Bivalvia: The animals of this class have indistinct heads, n eyes, tentacles, jaws and radula.
Cephalopoda- It has marine and free swimming organisms that are bilaterally symmetrical. They are dioecious and the development is also direct.

Hence, the correct answer is option (B).

Note: Pearls are prized as gems from ancient times. Kokichi Mikimoto of Toba is known as the Father of the Pearl industry. He developed the method to induce foreign particles into the mantle of the oyster to form pearls.