The word Mollusca is derived from the Latin word molluscus meaning soft. Mollusca are the animals whose body is soft, asymmetrical or bilaterally symmetrical, segmentless, ciliated, fleshy legs and exoskeleton made of calcium carbonate. Mollusca is the second largest phylum of fauna. But it is the largest marine episode. 23% of the ocean is molluscs. Precious pearls, Tyrian purple dye, sea silk, lime etc. are obtained from animals of this phase. The giant squid of this episode is 12 meters long and weighs 270 kg. Land snails (Achatina fulica) and snails cause extensive damage to crops and are known as crop pests. The number of species in this category is about 1,00,000. Johnston (1650) named the order Mollusca.