Phylum Mollusca - Practice Questions & MCQ

• The term ‘Mollusca’ is obtained from the Latin word molluscus that means soft-bodied. The phylum contains soft-bodied animals
• It is the second largest phylum of Kingdom Animalia with 60,000 species documented.
• They are mostly marine. However, they are also found in freshwater and on land
• They have organ system level of organization
• They have a true coelom but the coelom is greatly reduced. They are triploblastic
• They are bilaterally symmetrical
• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Seahare), Dentalium (Tusk shell) and Chaetopleura (Chiton).

Body Plan of Mollusca:

• Molluscs are unsegmented animals. 
• The body may have a covering of hard calcareous shell. The body can be distinguished into three different parts as:
• Head - sensory organs and mouth are present here
• Muscular foot - used for locomotion
• Visceral hump - dorsally placed and contains digestive system, excretory system and heart.
• There is a soft and spongy layer of skin over the visceral hump called mantle. 
• This mantle secretes calcium carbonate shell on its outer surface.
• The space between the visceral hump and mantle is called mantle cavity. Gills are present in this cavity.These help in Respiration and Excretion 
• The general body plan of molluscs can be shown as follows: