Caenogastropods are the most diverse group of living gastropods with about 157 extant families recognized. Caenogastropods include some of the largest and smallest gastropods, with shells ranging in adult size from about 1 to over 900 mm in length. They include many of the most colourful shelled -gastropods, some having elaborate markings and patterns on the shell and/or external animal. Caenogastropods were treated as a subset of ‘prosobranchs’, comprising most of the ‘Mesogastropoda’ and all the ‘Stenoglossa’. Some major groups of caenogastropods are recognised and supported in phylogenetic treatments, but the detailed relationships within those groups remain largely unresolved. A ‘fusiform’ shape is common, being determined by a feature unique to many caenogastropods – a canal in the anterior end of the aperture. The columella sometimes bears folds or plaits, a feature not uncommon in neogastropods but less common in other caenogastropods. The function of these folds remains controversial.