Phylum-Mollusca is divided into

Phylum-Mollusca is divided into Six classes.
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks.
The phylum is typically divided into six taxonomic classes, of which two are entirely extinct. Cephalopod molluscs, such as squid, cuttlefish, and octopuses, are among the most neurologically advanced of all invertebrates and either the giant squid or the colossal squid is the largest known invertebrate species.
The gastropods (snails and slugs) are by far the most numerous molluscs and account for 80% of the total classified species.