This is volume 5 in an eight-volume work, which provides a systematic account of more than 800 recognized species in the class Mollusca. This text deals with the completion of the family Ischnochitonidae and a revision of the family Mopaliidae. Earlier volumes in the series are updated in a preliminary 40 pages of additions. This volume describes 141 species, all of which are depicted in detail in drawings by the senior author. More than 50 maps show the worldwide distribution of every species. Descriptions are accompanied by a complete bibliography and synonymy. The text should be useful for workers in the field, professionals as well as advanced students.