Question

In Mollusca, eye present over a stalk, called as
A. Osphradium
B. Ostracum
C. Ommatophore
D. Operculum

Answer 1

The body of molluscs is often enclosed within a hard skeleton or shell. Their bodies are subsequently divided into different parts including a visceral mass, head and foot regions. Molluscs have eyes varying from simple structure to complexier structures.

Complete answer:
In certain molluscs such as Pila (Apple Snail), there is an olfactory sense organ called Osphradium. It is usually six to seven millimeters long, and has an elongated oval shape. This chemoreceptive sense organ is useful for monitoring the water currents that enters the mantle cavity of molluscs.
Ostracum is a part of the shell of the molluscs. It is usually the middle layer of the shell, which is meant for protecting an organism or structures enclosed within it.
The eyestalk which is a protrusion extending the eye in mollusca away from the body is generally called Ommatophore. It appears like a stumpy peduncle, on which eyes are located in molluscs. This is helpful in providing a better field of vision to the organisms such as snails (molluscs).
Operculum is a flexible bony plate providing protection to the sensitive gills of an aquatic organism. Thus, it is sometimes referred to as the gill cover. On inhalation of water through mouth, it is passed over the gills and is then exhaled from beneath this gill cover or operculum.

Hence, the correct answer is (C).

Note:
Mollusca is a phylum under the kingdom “Animalia” that constitutes animals having soft bodies. These animals often occur in almost every habitat present on the planet Earth. Squids, sea slugs, scallops, octopus, and snails are common examples of molluscs.