Final answer:
The class Gastropoda is the major clade of mollusk that is the most diverse in terms of the greatest number of species.
Step-by-step explanation:
The major clade of mollusk that is the most diverse in terms of the greatest number of species is the class Gastropoda.
Gastropods include snails, slugs, and nudibranchs, and they are the largest and most diverse class of mollusks, with over 60,000 described species.
Examples of gastropods include garden snails, sea slugs, and conch shells.