Question

Osphradium is
(a) Gustatory receptor
(b) Tangoreceptor
(c) Olfactory receptor
(d) Photoreceptor

Answer 1

Hint: Mollusc is marine water animal with segmented body form. They are bilaterally symmetrical with the organ system level of organisation. In mollusc, eyes and tentacles are present on the head with the presence of statocyst.

Complete Answer:
Osphradium is an olfactory receptor present in some molluscs, useful for testing the chemical and physical nature of water. Osphradium is linked with the respiratory organ of a mollusc.
A characteristic feature of the mollusc are,
The body structure of mollusc consists of a mantle made up of calcium carbonate, some molluscs have shells internally while some mollusc has shells externally. The mantle is a thin fleshy fold of dorsal wall. The epidermis is a single layer ciliated. The digestive tract is complete and the blood vascular system is of the open type with dorsal heart, arteries and veins, blood is blue colour due to the presence of copper. Gills and kidney work as excretory organs and ammonia is the chief excretory matter, the kidney is also known as Organ of Bojanus in some molluscs. Sexes are separate and development is either direct or indirect. Mollusc is divided into six classes monoplacophora, amphineura, Scaphopoda, Gastropoda, pelecypods, and Cephalopoda.
Osphradium is regressed in some Scaphopoda, Gastropods and cephalopods. The pluricellular mantle in the cuticle of these molluscs works as a photoreceptor. In case of pelecypods head, tentacles and eyes are absent, whereas gills are evolved into ctenidia for breathing and feeding.
So, the correct answer is the ‘(c) Olfactory receptor’.

Note: Annelids are the evolutionary precursor of a mollusc. Neoprene has first discovered mollusc with metameric segmentation and trochophore larvae. The similarity in these two characters proves that mollusc is descended from Annelids.