Question

How is the molluscs' mantle related to its shell?

Answer 1

The phylum Mollusca consists of soft-bodied animals, which are mostly marine but some also occur in freshwater and damp soil. The body of molluscs is unsegmented, shows bilateral symmetry, triploblastic and organ-system level of organisation is present.

Complete answer:
The body of molluscs consists of head, visceral mass and foot. Mantles cover the body. Mantle is a thin, fleshly fold of dorsal body wall more or less covering the body. It encloses a space between itself and the body which is known as mantle cavity (pallial cavity). Shell of the molluscs is an exoskeleton, secreted by the mantle. It is made up of calcium carbonate. the shell can be external and internal (e.g., slug, cuttlefish, slug). Most of the molluscs have an external shell. In some cases, such as Octopus, the shell is absent. Shell is protective in function. It protects the soft animals from predation and desiccation. Different species of molluscs exhibit different shapes of shells.

Additional information:
Molluscs are the second largest animal phylum after Arthropoda. They form an ancient group that have lived over 500 million years. Digestive tract is complete in molluscs and the blood vascular system is of open type. A copper-containing blue respiratory pigment called hemocyanin is found in blood which makes the colour of the blood blue. For aquatic respiration, well advanced gills are present. Annelids are known to be evolutionary precursors of molluscs.

Note: Pearl is actually an ‘inside out’ tiny shell secreted by bivalve like clam and oyster in response to an injury, parasite or foreign substances like sand or grain. Oyster is sedentary mollusc which is reared artificially for pearls.