Question

The basis of classification of phylum Mollusca is
A. Morphology
B. Respiratory organs
C. Both a and b
D. Shell

Answer 1

Hint: They are very diverse animals and they make up a significant part of the ecosystem. They have around 85,000 species with so many forms. Here in the question they are asking about the basis of classification of phylum Mollusca. Classification simply means to categorize something and phylum is the one category that comes under the hierarchy distribution.

Complete answer:
Molluscs have smooth bodies, they are bilaterally symmetrical animals. They usually have shells with a mantle, ventral foot, anterior head and visceral dorsal mass. They have tissue-level body organization.
They are mostly marine and few of them are freshwater and some are also terrestrial. They have very diverse sizes and shapes. They have two radula and mantle characters.
Their body is covered with ciliated single-layered epidermis. Mantle in them is like a fold of a wall that leaves the mantle cavity. They can respire through gills, lungs or both. And excretion takes place by paired kidneys (metanephridia).
They are classified mainly on the basis of the structure of shell or structure of radula. Radula is that part of the mouth which helps in the process of feeding.

Therefore, the correct answer is option (d).

Note:
Mollusca phylum can be divided into seven further classes which are- Monoplacophora, Aplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda and Scaphopoda. Examples of mollusca include octopuses, oysters, squids, snails, mussels etc. They can also be found inside the body of other animals like parasites. Within the mollusca, natural pearls are produced. They undergo sexual reproduction.