Question

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

Answer 1

Mollusca is one of the phyla of Animal Kingdom with triploblastic and coelomate animals. Some species undergo torsion. The sensory organs include the eyes, statocysts, and osphradia.

Complete answer:
Mollusca is the second-largest animal phylum. Molluscs are triploblastic, coelomate (schizocoelic) organisms with organ system level of organization. They have bilateral symmetry, but some are asymmetrical due to torsion as they grow. They have a tube within a tube body plan.

The body is soft and unsegmented, divisible into the head with sensory tentacles, foot, and visceral hump( contain digestive tract and other visceral organs). The soft body is covered by a fleshy fold called mantle/pallium. The mantle cavity is present between the visceral hump and mantle. Mantle secretes a calcareous shell (conchiolin matrix and calcite and aragonite) on its outer surface in some species.

Sensory organ eye is present over a movable stalk, known as ommatophore.
Osphradium is a chemoreceptor to test the physical and chemical nature of water.
The operculum is a lid-like structure, present in animals(other than humans).

So, the correct option is D. Ommatophore.

Note: In Mollusca, respiration is carried out by feather-like gills (ctenidia) in the mantle cavity or pulmonary chamber. Gills also help in excretion. The digestive system is well developed. It contains a rasping organ called radula for feeding. The excretory organ is one or two pairs of kidneys. The nervous system consists of paired ganglia. They are usually dioecious and oviparous with indirect development.